Faculty Publications: January, 2018

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Title:
Water facilitates oxygen migration on gold surfaces
Authors:
Xu, Fang; Fampiou, Ioanna; O'Connor, Christopher R.; Karakalos, Stavros; Hiebel, Fanny; Kaxiras, Efthimios; Madix, Robert J.; Friend, Cynthia M.
Affiliation:
AC(0000-0002-9224-9342), AD(0000-0002-3428-5433), AH(0000-0002-8673-9046)
Publication:
Physical Chemistry Chemical Physics, vol. 20, issue 4, pp. 2196-2204
Publication Date:
00/2018
Origin:
CROSSREF
DOI:
10.1039/C7CP06451A
Bibliographic Code:
2018PCCP...20.2196X

Abstract

Not Available

 

Title:
Probing the small-scale structure in strongly lensed systems via transdimensional inference
Authors:
Daylan, Tansu; Cyr-Racine, Francis-Yan; Diaz Rivero, Ana; Dvorkin, Cora; Finkbeiner, Douglas
Publication:
American Astronomical Society, AAS Meeting #231, id.#327.03
Publication Date:
01/2018
Origin:
AAS
Abstract Copyright:
(c) 2018: American Astronomical Society
Bibliographic Code:
2018AAS...23132703D

Abstract

Strong lensing is a sensitive probe of the small-scale density fluctuations in the Universe. We implement a novel approach to modeling strongly lensed systems using probabilistic cataloging, which is a transdimensional, hierarchical, and Bayesian framework to sample from a metamodel (union of models with different dimensionality) consistent with observed photon count maps. Probabilistic cataloging allows us to robustly characterize modeling covariances within and across lens models with different numbers of subhalos. Unlike traditional cataloging of subhalos, it does not require model subhalos to improve the goodness of fit above the detection threshold. Instead, it allows the exploitation of all information contained in the photon count maps, for instance, when constraining the subhalo mass function. We further show that, by not including these small subhalos in the lens model, fixed-dimensional inference methods can significantly mismodel the data. Using a simulated Hubble Space Telescope (HST) dataset, we show that the subhalo mass function can be probed even when many subhalos in the sample catalogs are individually below the detection threshold and would be absent in a traditional catalog. With the planned Wide Field Infrared Space Telescope (WFIRST), simultaneous probabilistic cataloging of dark subhalos in high-resolution, deep strong lens images has the potential to constrain the subhalo mass function at even lower masses.

 

Title:
A New 3D Map of Milky Way Dust
Authors:
Green, Gregory Maurice; Schlafly, Edward; Finkbeiner, Douglas
Affiliation:
AA(Stanford/KIPAC), AB(Lawrence Berkeley Laboratory), AC(Harvard Astronomy/Physics)
Publication:
American Astronomical Society, AAS Meeting #231, id.#350.02
Publication Date:
01/2018
Origin:
AAS
Abstract Copyright:
(c) 2018: American Astronomical Society
Bibliographic Code:
2018AAS...23135002G

Abstract

Interstellar dust is an important foreground for observations across a wide range of wavelengths. Dust grains scatter and absorb UV, optical and near-infrared light. These processes heat dust grains, causing them to radiate in the far-infrared. As a tracer of mass in the interstellar medium, dust correlates strongly with diffuse gamma-ray emission generated by cosmic-ray pion production. Thus, while dust makes up just 1% of the mass of the interstellar medium, it plays an outsize role in our efforts to address questions as diverse as the chemical evolution of the Milky Way galaxy and the existence of primordial B-mode polarizations in the CMB.We present a new 3D map of Milky Way dust, covering three-quarters of the sky (δ > -30°). The map is based on high-quality photometry of more than 800 million stars observed by Pan-STARRS 1, with matched photometry from 2MASS for approximately 200 million stars. We infer the distribution of dust vs. distance along sightlines with a typical angular scale of 6'. Out of the midplane of the Galaxy, our map agrees well with 2D maps based on far-infrared dust emission. After accounting for a 15% difference in scale, we find a mean scatter of approximately 10% between our map and the Planck 2D dust map, out to a depth of 0.8 mag in E(r-z). Our map can be downloaded at http://argonaut.skymaps.info.In order to extend our map, we have surveyed the southern Galactic plane with DECam, which is mounted on the 4m Blanco telescope on Cerro Tololo. The resulting survey, the Dark Energy Camera Plane Survey (DECaPS), is now publicly available. See Edward Schlafly's poster for more information on DECaPS.

 

Title:
The DECam Plane Survey: Optical photometry of two billion objects in the southern Galactic plane
Authors:
Schlafly, Edward; Green, Gregory M.; Lang, Dustin; Daylan, Tansu; Finkbeiner, Douglas; Lee, Albert; Meisner, Aaron; Schlegel, David; Valdes, Francisco
Publication:
American Astronomical Society, AAS Meeting #231, id.#354.01
Publication Date:
01/2018
Origin:
AAS
Abstract Copyright:
(c) 2018: American Astronomical Society
Bibliographic Code:
2018AAS...23135401S

Abstract

The DECam Plane Survey is a five-band optical and near-infrared survey of the southern Galactic plane with the Dark Energy Camera at Cerro Tololo. The survey is designed to reach past the main-sequence turn-off at the distance of the Galactic center through a reddening E(B-V) of 1.5 mag. Typical single-exposure depths are 23.7, 22.8, 22.3, 21.9, and 21.0 mag in the grizY bands, with seeing around 1 arcsecond. The footprint covers the Galactic plane with |b| < 4°, 5° > l > -120°. The survey pipeline simultaneously solves for the positions and fluxes of tens of thousands of sources in each image, delivering positions and fluxes of roughly two billion stars with better than 10 mmag precision. Most of these objects are highly reddened and deep in the Galactic disk, probing the structure and properties of the Milky Way and its interstellar medium. The full survey is publicly available.

 

Title:
Induced Ellipticity for Inspiraling Binary Systems
Authors:
Randall, Lisa; Xianyu, Zhong-Zhi
Publication:
The Astrophysical Journal, Volume 853, Issue 1, article id. 93, 13 pp. (2018). (ApJ Homepage)
Publication Date:
01/2018
Origin:
IOP
Astronomy Keywords:
binaries: close, gravitational waves
DOI:
10.3847/1538-4357/aaa1a2
Bibliographic Code:
2018ApJ...853...93R

Abstract

Although gravitational waves tend to erase eccentricity of an inspiraling binary system, ellipticity can be generated in the presence of surrounding matter. We present a semianalytical method for understanding the eccentricity distribution of binary black holes (BHs) in the presence of a supermassive BH in a galactic center. Given a matter distribution, we show how to determine the resultant eccentricity analytically in the presence of both tidal forces and evaporation up to one cutoff and one matter-distribution-independent function, paving the way for understanding the environment of detected inspiraling BHs. We furthermore generalize Kozai–Lidov dynamics to situations where perturbation theory breaks down for short time intervals, allowing more general angular momentum exchange, such that eccentricity is generated even when all bodies orbit in the same plane.

 

Title:
Topological order and Fermi surface reconstruction
Authors:
Sachdev, Subir
Publication:
eprint arXiv:1801.01125
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory, Quantum Physics
Comment:
48 pages, 22 figures. Review article, comments welcome. Partly based on lectures at the 34th Jerusalem Winter School in Theoretical Physics: New Horizons in Quantum Matter, December 27, 2016 - January 5, 2017, https://tinyurl.com/y8oglg4e ;(v2) added refs, figures, remarks
Bibliographic Code:
2018arXiv180101125S

Abstract

This review describes how topological order can reconstruct Fermi surfaces of metals, even in the absence of translational symmetry breaking. We begin with an introduction to topological order using Wegner's quantum $\mathbb{Z}_2$ gauge theory on the square lattice: the topological state is characterized by the expulsion of defects, carrying $\mathbb{Z}_2$ magnetic flux. The interplay between topological order and the breaking of global symmetry is described by the non-zero temperature statistical mechanics of classical XY models in dimension $D=3$; such models also describe the zero temperature quantum phases of bosons with short-range interactions on the square lattice at integer filling. The topological state is again characterized by the expulsion of certain defects, in a state with fluctuating symmetry-breaking order. The phase diagrams of the $\mathbb{Z}_2$ gauge theory and the XY models are obtained by embedding them in U(1) gauge theories, and by studying their Higgs and confining phases. These ideas are then applied to the single-band Hubbard model on the square lattice. A SU(2) gauge theory describes the fluctuations of spin-density-wave order, and its phase diagram is presented by analogy to the XY models. We obtain a class of zero temperature metallic states with fluctuating spin-density wave order, topological order associated with defect expulsion, reconstructed Fermi surfaces (with `chargon' or electron-like quasiparticles), but no broken symmetry. We conclude with the application of such metallic states to the pseudogap phase of the cuprates, and note the recent comparison with numerical studies of the Hubbard model. In a detour, we also discuss the influence of Berry phases, and how they can lead to deconfined quantum critical points: this applies to bosons on the square lattice at half-integer filling, and to quantum dimer models.

 

Title:
Exploring the Kondo model in and out of equilibrium with alkaline-earth atoms
Authors:
Kanász-Nagy, Márton; Ashida, Yuto; Shi, Tao; Pascu Moca, Catalin; Ikeda, Tatsuhiko N.; Fölling, Simon; Cirac, J. Ignacio; Zaránd, Gergely; Demler, Eugene A.
Publication:
eprint arXiv:1801.01132
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Quantum Gases, Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons, Quantum Physics
Comment:
22 pages, 12 figures
Bibliographic Code:
2018arXiv180101132K

Abstract

We propose a scheme to realize the Kondo model with tunable anisotropy using alkaline-earth atoms in an optical lattice. The new feature of our setup is Floquet engineering of interactions using time-dependent Zeeman shifts, that can be realized either using state-dependent optical Stark shifts or magnetic fields. The properties of the resulting Kondo model strongly depend on the anisotropy of the ferromagnetic interactions. In particular, easy-plane couplings give rise to Kondo singlet formation even though microscopic interactions are all ferromagnetic. We discuss both equilibrium and dynamical properties of the system that can be measured with ultracold atoms, including the impurity spin susceptibility, the impurity spin relaxation rate, as well as the equilibrium and dynamical spin correlations between the impurity and the ferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the system using a variational non-Gaussian approach, which allows us to explore coherent dynamics over both short and long timescales, as set by the bandwidth and the Kondo singlet formation, respectively. In the quench-type experiments, when the Kondo interaction is suddenly switched on, we find that real-time dynamics shows crossovers reminiscent of poor man's renormalization group flow used to describe equilibrium systems. For bare easy-plane ferromagnetic couplings, this allows us to follow the formation of the Kondo screening cloud as the dynamics crosses over from ferromagnetic to antiferromagnetic behavior. On the other side of the phase diagram, our scheme makes it possible to measure quantum corrections to the well-known Korringa law describing the temperature dependence of the impurity spin relaxation rate. Theoretical results discussed in our paper can be measured using currently available experimental techniques.

 

Title:
Factorization Violation and Scale Invariance
Authors:
Schwartz, Matthew D.; Yan, Kai; Zhu, Hua Xing
Publication:
eprint arXiv:1801.01138
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology
Comment:
36 pages, 15 figures
Bibliographic Code:
2018arXiv180101138S

Abstract

Factorization violating effects in hadron scattering are due mainly to spectator-spectator interactions. While it is known that these interactions cancel in inclusive cross sections, like for the Drell-Yan process, not much is known about for what classes of observables factorization is violated. We show that for pure Glauber ladder graphs, all amplitude-level factorization violating effects completely cancel at cross section level for any single-scale observable (such as hadronic transverse energy or beam thrust). This result disproves previous claims that these pure Glauber graphs are factorization-violating. Our proof exploits scale invariance of two-to-two scattering amplitudes in an essential way. The leading factorization-violating effects therefore come from graphs with at least one soft gluon, involving the Lipatov vertex off of the Glauber ladders. This implies that real soft radiation must be involved in factorization-violation, shedding light on the connection between factorization-violation and the underlying event.

 

Title:
Hasse-Witt matrices, unit roots and period integrals
Authors:
Huang, An; Lian, Bong; Yau, Shing-Tung; Yu, Chenglong
Publication:
eprint arXiv:1801.01189
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, Mathematics - Number Theory, 14G10, 32G20
Comment:
26 pages
Bibliographic Code:
2018arXiv180101189H

Abstract

Motivated by the work of Candelas, de la Ossa and Rodriguez-Villegas [6], we study the relations between Hasse-Witt matrices and period integrals of Calabi-Yau hypersurfaces in both toric varieties and partial flag varieties. We prove a conjecture by Vlasenko [23] on higher Hasse-Witt matrices for toric hypersurfaces following Katz's method of local expansion [14, 15]. The higher Hasse-Witt matrices also have close relation with period integrals. The proof gives a way to pass from Katz's congruence relations in terms of expansion coefficients [15] to Dwork's congruence relations [8] about periods.

 

Title:
Period integrals of local complete intersections and tautological systems
Authors:
Huang, An; Lian, Bong; Yau, Shing-Tung; Yu, Chenglong
Publication:
eprint arXiv:1801.01194
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, 32G20
Comment:
14 pages
Bibliographic Code:
2018arXiv180101194H

Abstract

Tautological systems developed in [6],[7] are Picard-Fuchs type systems to study period integrals of complete intersections in Fano varieties. We generalize tautological systems to local complete intersections, which are zero loci of global sections of vector bundles over Fano varieties. In particular, we obtain similar criterion as [6, 7] about holonomicity and regularity of the system. We also prove solution rank formulas and geometric realizations of solutions following the work of hypersurfaces [5, 4].

 

Title:
Phonon networks with SiV centers in diamond waveguides
Authors:
Lemonde, M.-A.; Meesala, S.; Sipahigil, A.; Schuetz, M. J. A.; Lukin, M. D.; Loncar, M.; Rabl, P.
Publication:
eprint arXiv:1801.01904
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Quantum Physics
Comment:
4.5 pages of main text with 4 figures. 14 pages of Supplemental informations with 3 figures
Bibliographic Code:
2018arXiv180101904L

Abstract

We propose and analyze a novel realization of a solid-state quantum network, where separated silicon-vacancy centers are coupled via the phonon modes of a quasi-1D diamond waveguide. In our approach, quantum states encoded in long-lived electronic spin states can be converted into propagating phonon wavepackets and be reabsorbed efficiently by a distant defect center. Our analysis shows that under realistic conditions, this approach enables the implementation of high-fidelity, scalable quantum communication protocols within chip-scale spin-qubit networks. Apart from quantum information processing, this setup constitutes a novel waveguide QED platform, where strong-coupling effects between solid-state defects and individual propagating phonons can be explored at the quantum level.

 

Title:
Galactic Reddening in 3D from Stellar Photometry - An Improved Map
Authors:
Green, Gregory M.; Schlafly, Edward F.; Finkbeiner, Douglas; Rix, Hans-Walter; Martin, Nicolas; Burgett, William; Draper, Peter W.; Flewelling, Heather; Hodapp, Klaus; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Metcalfe, Nigel; Tonry, John L.; Wainscoat, Richard; Waters, Christopher
Publication:
eprint arXiv:1801.03555
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Astrophysics - Astrophysics of Galaxies
Comment:
Submitted to MNRAS. 17 pages, 16 figures
Bibliographic Code:
2018arXiv180103555G

Abstract

We present a new 3D map of interstellar dust reddening, covering three quarters of the sky (declinations greater than -30 degrees) out to a distance of several kiloparsecs. The map is based on high-quality stellar photometry of 800 million stars from Pan-STARRS 1 and 2MASS. We divide the sky into sightlines containing a few hundred stars each, and then infer stellar distances and types, along with the line-of-sight dust distribution. Our new map incorporates a more accurate average extinction law and an additional 1.5 years of Pan-STARRS 1 data, tracing dust to greater extinctions and at higher angular resolutions than our previous map. Out of the plane of the Galaxy, our map agrees well with 2D reddening maps derived from far-infrared dust emission. After accounting for a 15% difference in scale, we find a mean scatter of 10% between our map and the Planck far-infrared emission-based dust map, out to a depth of 0.8 mag in E(r-z), with the level of agreement varying over the sky. Our map can be downloaded at http://argonaut.skymaps.info, or by its DOI: 10.7910/DVN/LCYHJG.

 

Title:
Tuning methods for semiconductor spin--qubits
Authors:
Botzem, Tim; Shulman, Michael D.; Foletti, Sandra; Harvey, Shannon P.; Dial, Oliver E.; Bethke, Patrick; Cerfontaine, Pascal; McNeil, Robert P. G.; Mahalu, Diana; Umansky, Vladimir; Ludwig, Arne; Wieck, Andreas; Schuh, Dieter; Bougeard, Dominique; Yacoby, Amir; Bluhm, Hendrik
Publication:
eprint arXiv:1801.03755
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2018arXiv180103755B

Abstract

We present efficient methods to reliably characterize and tune gate-defined semiconductor spin qubits. Our methods are designed to target the tuning procedures of semiconductor double quantum dot in GaAs heterostructures, but can easily be adapted to other quantum-dot-like qubit systems. These tuning procedures include the characterization of the inter-dot tunnel coupling, the tunnel coupling to the surrounding leads and the identification of the various fast initialization points for the operation of the qubit. Since semiconductor-based spin qubits are compatible with standard semiconductor process technology and hence promise good prospects of scalability, the challenge of efficiently tuning the dot's parameters will only grow in the near future, once the multi-qubit stage is reached. With the anticipation of being used as the basis for future automated tuning protocols, all measurements presented here are fast-to-execute and easy-to-analyze characterization methods. They result in quantitative measures of the relevant qubit parameters within a couple of seconds, and require almost no human interference.

 

Title:
Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control
Authors:
Bauch, Erik; Hart, Connor A.; Schloss, Jennifer M.; Turner, Matthew J.; Barry, John F.; Kehayias, Pauli; Singh, Swati; Walsworth, Ronald L.
Publication:
eprint arXiv:1801.03793
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Quantum Physics
Bibliographic Code:
2018arXiv180103793B

Abstract

Quantum spin dephasing is caused by inhomogeneous coupling to the environment, with resulting limits to the measurement time and precision of spin-based sensors. The effects of spin dephasing can be especially pernicious for dense ensembles of electronic spins in the solid-state, such as for nitrogen-vacancy (NV) color centers in diamond. We report the use of two complementary techniques, spin bath control and double quantum coherence, to enhance the inhomogeneous spin dephasing time ($T_2^*$) for NV ensembles by more than an order of magnitude. In combination, these quantum control techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing mechanisms, including crystal strain gradients and dipolar interactions with paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio by a factor of two. Applied independently, spin bath control and double quantum coherence elucidate the sources of spin dephasing over a wide range of NV and spin bath concentrations. These results demonstrate the longest reported $T_2^*$ in a solid-state electronic spin ensemble at room temperature, and outline a path towards NV-diamond magnetometers with broadband femtotesla sensitivity.

 

Title:
On Geometric Classification of 5d SCFTs
Authors:
Jefferson, Patrick; Katz, Sheldon; Kim, Hee-Cheol; Vafa, Cumrun
Publication:
eprint arXiv:1801.04036
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematics - Algebraic Geometry
Comment:
66 pages + appendices. v2: Included additional references, corrected minor typos
Bibliographic Code:
2018arXiv180104036J

Abstract

We formulate geometric conditions necessary for engineering 5d superconformal field theories (SCFTs) via M-theory compactification on a local Calabi-Yau 3-fold. Extending the classification of the rank 1 cases, which are realized geometrically as shrinking del Pezzo surfaces embedded in a 3-fold, we propose an exhaustive classification of local 3-folds engineering rank 2 SCFTs in 5d. This systematic classification confirms that all rank 2 SCFTs predicted using gauge theoretic arguments can be realized as consistent theories, with the exception of one family which is shown to be non-perturbatively inconsistent and thereby ruled out by geometric considerations. We find that all rank 2 SCFTs descend from 6d (1,0) SCFTs compactified on a circle possibly twisted with an automorphism together with holonomies for global symmetries around the Kaluza-Klein circle. These results support our conjecture that every 5d SCFT can be obtained from the circle compactification of some parent 6d (1,0) SCFT.

 

Title:
Coupling Two Spin Qubits with a High-Impedance Resonator
Authors:
Harvey, S. P.; Bøttcher, C. G. L.; Orona, L. A.; Bartlett, S. D.; Doherty, A. C.; Yacoby, A.
Publication:
eprint arXiv:1801.04858
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
15 pages, 2 figures
Bibliographic Code:
2018arXiv180104858H

Abstract

Fast, high-fidelity single and two-qubit gates are essential to building a viable quantum information processor, but achieving both in the same system has proved challenging for spin qubits. We propose and analyze an approach to perform a long-distance two-qubit controlled phase (CPHASE) gate between two singlet-triplet qubits using an electromagnetic resonator to mediate their interaction. The qubits couple longitudinally to the resonator, and by driving the qubits near the resonator's frequency they can be made to acquire a state-dependent geometric phase that leads to a CPHASE gate independent of the initial state of the resonator. Using high impedance resonators enables gate times of order 10 ns while maintaining long coherence times. Simulations show average gate fidelities of over 96% using currently achievable experimental parameters and over 99% using state-of-the-art resonator technology. After optimizing the gate fidelity in terms of parameters tuneable in-situ, we find it takes a simple power-law form in terms of the resonator's impedance and quality and the qubits' noise bath.

 

Title:
Tunneling Topological Vacua via Extended Operators: TQFT Spectra and Boundary Deconfinement in Various Dimensions
Authors:
Wang, Juven; Ohmori, Kantaro; Putrov, Pavel; Zheng, Yunqin; Lin, Hai; Gao, Peng; Yau, Shing-Tung
Publication:
eprint arXiv:1801.05416
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, High Energy Physics - Theory, Mathematical Physics
Comment:
52 pages, 8 figures, 7 tables
Bibliographic Code:
2018arXiv180105416W

Abstract

Distinct quantum vacua of topologically ordered states can be tunneled into each other via extended operators. The possible applications include condensed matter and quantum cosmology. We present a straightforward approach to calculate the partition function on various manifolds and ground state degeneracy (GSD), mainly based on continuum/cochain Topological Quantum Field Theories (TQFT), in any dimensions. This information can be related to the counting of extended operators of bosonic/fermionic TQFT. On the lattice scale, anyonic particles/strings live at the ends of line/surface operators. Certain systems in different dimensions are related to each other through dimensional reduction schemes, analogous to decategorification. We consider situations where a TQFT lives on (1) a closed spacetime or (2) a spacetime with boundary, such that both the bulk and boundary are fully-gapped and long-range entangled (LRE). Anyonic excitations can be deconfined on the boundary. We describe such new exotic topological interfaces on which neither particle nor string excitation alone condensed, but only composite objects of extended operators can end (e.g. a string-like composite object formed by a set of particles can end on a special 2+1D boundary of 3+1D bulk). We explore the relations between group extension constructions and partially breaking constructions (e.g. 0-form/higher-form/"composite" breaking) of topological boundaries, after gauging. We comment on the implications of entanglement entropy for some of such LRE systems.

 

Title:
Controlling polyelectrolyte adsorption onto carbon nanotubes by tuning ion-image interactions
Authors:
Lee, Alpha A.; Kostinski, Sarah V.; Brenner, Michael P.
Publication:
eprint arXiv:1801.05635
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter, Condensed Matter - Statistical Mechanics, Physics - Chemical Physics
Comment:
This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry B. To access the final edited and published work see http://www.pubs.acs.org/doi/10.1021/acs.jpcb.7b11398; doi:10.1021/acs.jpcb.7b11398
Bibliographic Code:
2018arXiv180105635L

Abstract

Understanding and controlling polyelectrolyte adsorption onto carbon nanotubes is a fundamen- tal challenge in nanotechology. Polyelectrolytes have been shown to stabilise nanotube suspensions through adsorbing onto the nanotube surface, and polyelectrolyte-coated nanotubes are emerging as building blocks for complex and addressable self-assembly. The conventional wisdom suggests that polyelectrolyte adsorption onto nanotubes is driven by specific chemical or van der Waals interac- tions. We develop a simple mean-field model and show that ion-image attraction is a significant effect for adsorption onto conducting nanotubes at low salt concentrations. Our theory suggests a simple strategy to selectively and reversibly functionalize carbon nanotubes based on their electronic structure which in turn modifies the ion-image attraction.

 

Title:
Solving quantum impurity problems in and out of equilibrium with variational approach
Authors:
Ashida, Yuto; Shi, Tao; Bañuls, Mari Carmen; Cirac, J. Ignacio; Demler, Eugene
Publication:
eprint arXiv:1801.05825
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Quantum Gases, Condensed Matter - Statistical Mechanics, Quantum Physics
Comment:
6 pages, 4 figures
Bibliographic Code:
2018arXiv180105825A

Abstract

An efficient variational approach is developed to solve in- and out-of-equilibrium problems of generic quantum spin-impurity systems. Employing the discrete symmetry hidden in spin-impurity models, we present a new canonical transformation that completely decouples the impurity and bath degrees of freedom. Combining it with Gaussian states, we present a family of many-body states to efficiently encode nontrivial impurity-bath correlations. We demonstrate its successful application to the anisotropic and two-lead Kondo models by studying their spatiotemporal dynamics, universal nonperturbative scaling and transport phenomena, and compare to other analytical and numerical approaches. In particular, we apply our method to study new types of nonequilibrium phenomena that have not been studied by other methods, such as long-time crossover in the ferromagnetic easy-plane Kondo model. Our results can be tested in experiments with mesoscopic electron systems and ultracold atoms in optical lattices.

 

Title:
Li-Yau inequality for unbounded Laplacian on graphs
Authors:
Gong, Chao; Lin, Yong; Liu, Shuang; Yau, Shing-Tung
Publication:
eprint arXiv:1801.06021
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Mathematics - Differential Geometry
Comment:
19 pages
Bibliographic Code:
2018arXiv180106021G

Abstract

In this paper, we derive Li-Yau inequality for unbounded Laplacian on complete weighted graphs with the assumption of the curvature-dimension inequality $CDE'(n,K)$, which can be regarded as a notion of curvature on graphs. Furthermore, we obtain some applications of Li-Yau inequality, including Harnack inequality, heat kernel bounds and Cheng's eigenvalue estimate. These are first kind of results on this direction for unbounded Laplacian on graphs.

 

Title:
Galaxy Bispectrum from Massive Spinning Particles
Authors:
Moradinezhad Dizgah, Azadeh; Lee, Hayden; Muñoz, Julian B.; Dvorkin, Cora
Publication:
eprint arXiv:1801.07265
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology
Bibliographic Code:
2018arXiv180107265M

Abstract

Massive spinning particles, if present during inflation, lead to a distinctive bispectrum of primordial perturbations, the shape and amplitude of which depend on the masses and spins of the extra particles. This signal, in turn, leaves an imprint in the statistical distribution of galaxies; in particular, as a non-vanishing galaxy bispectrum, which can be used to probe the masses and spins of these particles. In this paper, we present for the first time a new theoretical template for the bispectrum generated by massive spinning particles, valid for a general triangle configuration. We then proceed to perform a Fisher-matrix forecast to assess the potential of two next-generation spectroscopic galaxy surveys, EUCLID and DESI, to constrain the primordial non-Gaussianity sourced by these extra particles. We model the galaxy bispectrum using tree-level perturbation theory, accounting for redshift-space distortions and the Alcock-Paczynski effect, and forecast constraints on the primordial non-Gaussianity parameters marginalizing over all relevant biases and cosmological parameters. Our results suggest that these surveys would potentially be sensitive to any primordial non-Gaussianity with an amplitude larger than $f_{\rm NL}\approx 1$, for massive particles with spins 2, 3, and 4. Interestingly, if non-Gaussianities are present at that level, these surveys will be able to infer the masses of these spinning particles to within tens of percent. If detected, this would provide a very clear window into the particle content of our Universe during inflation.

 

Title:
Electronic Branched Flow in Graphene with Random Potential: Theory and Machine Learning Prediction
Authors:
Mattheakis, Marios; Tsironis, G. P.; Kaxiras, Efthimios
Publication:
eprint arXiv:1801.08217
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Nonlinear Sciences - Pattern Formation and Solitons, Physics - Computational Physics
Bibliographic Code:
2018arXiv180108217M

Abstract

We investigate the ultra-relativistic electronic flow in a two-dimensional random potential relevant to charge carrier dynamics in Dirac solids. As an example, the random potential in graphene, the prototypical Dirac solid, arises from inhomogeneous charge impurities in the substrate, a common feature in experimental systems. An additional bias voltage is introduce to tune the electronic propagation. We show that the onset of {electronic branched flow} is determined by the statistical properties of the potential and we provide a scaling-type relationship that describes the emergence of branches. We also show that, despite the statistical nature of branching, reservoir computing provides an accurate detection mechanism for the caustics. The onset of branching is predicted through a deep learning {algorithm}, which may be implemented experimentally to improve materials properties of graphene substrates.

 

Title:
Jacobian rings for homogenous vector bundles and applications
Authors:
Huang, An; Lian, Bong; Yau, Shing-Tung; Yu, Chenglong
Publication:
eprint arXiv:1801.08261
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Mathematics - Algebraic Geometry, 32G20
Comment:
19 pages
Bibliographic Code:
2018arXiv180108261H

Abstract

In this note, we examine the Jacobian ring description of the Hodge structure of zero loci of vector bundle sections on a class of ambient varieties. We consider a set of cohomological vanishing conditions that imply such a description, and we verify these conditions for some new cases. We also observe that the method can be directly extended to log homogeneous varieties. We apply the Jacobian ring to study the null varieties of period integrals and their derivatives, generalizing a result in [9] for projective spaces. As an additional application, we prove the Hodge conjecture for very generic hypersurfaces in certain generalized flag varieties.

 

Title:
Nonlinear mechanics of thin frames
Authors:
Moshe, Michael; Shankar, Suraj; Bowick, Mark J.; Nelson, David R.
Publication:
eprint arXiv:1801.08263
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Comment:
13 pages, 13 figures
Bibliographic Code:
2018arXiv180108263M

Abstract

The dramatic effect kirigami, such as hole cutting, has on the elastic properties of thin sheets invites a study of the mechanics of thin elastic frames under an external load. Such frames can be thought of as modular elements needed to build any kirigami pattern. Here we develop the technique of elastic charges to address a variety of elastic problems involving thin sheets with perforations, focusing on frames with sharp corners. We find that holes generate elastic defects (partial disclinations) which act as sources of geometric incompatibility. Numerical and analytic studies are made of three different aspects of loaded frames - the deformed configuration itself, the effective mechanical properties in the form of force-extension curves and the buckling transition triggered by defects. This allows us to understand generic kirigami mechanics in terms of a set of force-dependent elastic charges with long-range interactions.

 

Title:
Electrical generation and detection of spin waves in a quantum Hall ferromagnet
Authors:
Wei, Di. S.; van der Sar, Toeno; Lee, Seung Hwan; Watanabe, Kenji; Taniguchi, Takashi; Halperin, Bertrand I.; Yacoby, Amir
Publication:
eprint arXiv:1801.08534
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Bibliographic Code:
2018arXiv180108534W

Abstract

Spin waves are essential to understanding the intrinsic ordering and thermodynamic properties of magnetic systems. An attractive candidate for studying long-lived spin-wave physics is the quantum Hall (QH) ferromagnet, which forms spontaneously in clean two-dimensional electron systems at low temperature and in a perpendicular magnetic field. However, the charge-neutral nature of these elementary spin excitations has made them challenging to detect and study. Here we use out-of-equilibrium occupation of QH edge channels in graphene to excite and detect spin waves in magnetically ordered QH states. Our experiments provide direct evidence for long distance spin wave propagation through different ferromagnetic phases in the N=0 Landau level (LL), as well as across the insulating canted antiferromagnetic (CAF) phase. Our results open a new arena of experimental investigation into the fundamental magnetic properties of these exotic two-dimensional electron systems.

 

Title:
Strain engineering of the silicon-vacancy center in diamond
Authors:
Meesala, Srujan; Sohn, Young-Ik; Pingault, Benjamin; Shao, Linbo; Atikian, Haig A.; Holzgrafe, Jeffrey; Gundogan, Mustafa; Stavrakas, Camille; Sipahigil, Alp; Chia, Cleaven; Burek, Michael J.; Zhang, Mian; Wu, Lue; Pacheco, Jose L.; Abraham, John; Bielejec, Edward; Lukin, Mikhail D.; Atature, Mete; Loncar, Marko
Publication:
eprint arXiv:1801.09833
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
Quantum Physics, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
14 pages, 10 figures
Bibliographic Code:
2018arXiv180109833M

Abstract

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multi-qubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain suseptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.

 

Title:
Learning to Classify from Impure Samples
Authors:
Komiske, Patrick T.; Metodiev, Eric M.; Nachman, Benjamin; Schwartz, Matthew D.
Publication:
eprint arXiv:1801.10158
Publication Date:
01/2018
Origin:
ARXIV
Keywords:
High Energy Physics - Phenomenology, High Energy Physics - Experiment, Statistics - Machine Learning
Comment:
6 pages, 2 tables, 2 figures
Bibliographic Code:
2018arXiv180110158K

Abstract

A persistent challenge in practical classification tasks is that labelled training sets are not always available. In particle physics, this challenge is surmounted by the use of simulations. These simulations accurately reproduce most features of data, but cannot be trusted to capture all of the complex correlations exploitable by modern machine learning methods. Recent work in weakly supervised learning has shown that simple, low-dimensional classifiers can be trained using only the impure mixtures present in data. Here, we demonstrate that complex, high-dimensional classifiers can also be trained on impure mixtures using weak supervision techniques, with performance comparable to what could be achieved with pure samples. Using weak supervision will therefore allow us to avoid relying exclusively on simulations for high-dimensional classification. This work opens the door to a new regime whereby complex models are trained directly on data, providing direct access to probe the underlying physics.

 

Title:
Search for dark matter produced in association with bottom or top quarks in √{s}=13 TeV pp collisions with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;...
Publication:
The European Physical Journal C, Volume 78, Issue 1, article id. #18, 36 pp. (EPJC Homepage)
Publication Date:
01/2018
Origin:
SPRINGER
Abstract Copyright:
(c) 2018: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-5486-1
Bibliographic Code:
2018EPJC...78...18A

Abstract

A search for weakly interacting massive dark-matter particles produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and missing transverse momentum are considered. The analysis uses 36.1 fb^{-1} of proton-proton collision data recorded by the ATLAS experiment at √{s}=13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are interpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour-neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross-section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour-charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements.

 

Title:
Search for heavy resonances decaying into WW in the eν μ ν final state in pp collisions at √{s}=13 {TeV} with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;
Publication:
The European Physical Journal C, Volume 78, Issue 1, article id. #24, 34 pp. (EPJC Homepage)
Publication Date:
01/2018
Origin:
SPRINGER
Abstract Copyright:
(c) 2018: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-017-5491-4
Bibliographic Code:
2018EPJC...78...24A

Abstract

A search for neutral heavy resonances is performed in the WW→ eν μ ν decay channel using pp collision data corresponding to an integrated luminosity of 36.1 fb^{-1}, collected at a centre-of-mass energy of 13 {TeV} by the ATLAS detector at the Large Hadron Collider. No evidence of such heavy resonances is found. In the search for production via the quark-antiquark annihilation or gluon-gluon fusion process, upper limits on σ _X× B(X → WW) as a function of the resonance mass are obtained in the mass range between 200 {GeV} and up to 5 {TeV} for various benchmark models: a Higgs-like scalar in different width scenarios, a two-Higgs-doublet model, a heavy vector triplet model, and a warped extra dimensions model. In the vector-boson fusion process, constraints are also obtained on these resonances, as well as on a Higgs boson in the Georgi-Machacek model and a heavy tensor particle coupling only to gauge bosons.

 

Title:
E-String Theory on Riemann Surfaces
Authors:
Kim, Hee-Cheol; Razamat, Shlomo S.; Vafa, Cumrun; Zafrir, Gabi
Publication:
Fortschritte der Physik, vol. 66, issue 1, p. 1700074
Publication Date:
01/2018
Origin:
CROSSREF
DOI:
10.1002/prop.201700074
Bibliographic Code:
2018ForPh..66a0074K

Abstract

We study compactifications of the 6d E-string theory, the theory of a small E_8 instanton, to four dimensions. In particular we identify N=1 field theories in four dimensions corresponding to compactifications on arbitrary Riemann surfaces with punctures and with arbitrary non-abelian flat connections as well as fluxes for the abelian sub-groups of the E_8 flavor symmetry. This sheds light on emergent symmetries in a number of 4d N=1 SCFTs (including the `E7 surprise' theory) as well as leads to new predictions for a large number of 4-dimensional exceptional dualities and symmetries.

 

Title:
Scale-dependent galaxy bias from massive particles with spin during inflation
Authors:
Moradinezhad Dizgah, Azadeh; Dvorkin, Cora
Publication:
Journal of Cosmology and Astroparticle Physics, Issue 01, article id. 010 (2018). (JCAP Homepage)
Publication Date:
01/2018
Origin:
IOP
DOI:
10.1088/1475-7516/2018/01/010
Bibliographic Code:
2018JCAP...01..010M

Abstract

The presence of additional particles during inflation leads to non-Gaussianity in late-time correlators of primordial curvature perturbations. The shape and amplitude of this signal depend on the mass and spin of the extra particles. Constraints on this distinct form of primordial non-Gaussianity, therefore, provide a wealth of information on the particle content during inflation. We investigate the potential of upcoming galaxy surveys in constraining such a signature through its impact on the observed galaxy power spectrum. Primordial non-Gaussianity of various shapes induces a scale-dependent bias on tracers of large-scale structure, such as galaxies. Using this signature we obtain constraints on massive particles during inflation, which can have non-zero spins. In particular, we show that the prospects for constraining particles with spins 0 and 1 are promising, while constraining particles with spin 2 from power spectrum alone seems challenging. We show that the multi-tracer technique can significantly improve the constraints from the power spectrum by at least an order of magnitude. Furthermore, we analyze the effect of non-linearities due to gravitational evolution on the forecasted constraints on the masses of the extra particles and the amplitudes of the imprinted non-Gaussian signal. We find that gravitational evolution affects the constraints by less than a factor of 2.

 

Title:
ADE string chains and mirror symmetry
Authors:
Haghighat, Babak; Yan, Wenbin; Yau, Shing-Tung
Publication:
Journal of High Energy Physics, Volume 2018, Issue 1, article id. #43, 30 pp.
Publication Date:
01/2018
Origin:
SPRINGER
Keywords:
F-Theory, Field Theories in Higher Dimensions, Supersymmetric Gauge Theory, Topological Strings
Abstract Copyright:
(c) 2018: The Author(s)
DOI:
10.1007/JHEP01(2018)043
Bibliographic Code:
2018JHEP...01..043H

Abstract

6d superconformal field theories (SCFTs) are the SCFTs in the highest possible dimension. They can be geometrically engineered in F-theory by compactifying on non-compact elliptic Calabi-Yau manifolds. In this paper we focus on the class of SCFTs whose base geometry is determined by -2 curves intersecting according to ADE Dynkin diagrams and derive the corresponding mirror Calabi-Yau manifold. The mirror geometry is uniquely determined in terms of the mirror curve which has also an interpretation in terms of the Seiberg-Witten curve of the four-dimensional theory arising from torus compactification. Adding the affine node of the ADE quiver to the base geometry, we connect to recent results on SYZ mirror symmetry for the A case and provide a physical interpretation in terms of little string theory. Our results, however, go beyond this case as our construction naturally covers the D and E cases as well.

 

Title:
Search for additional heavy neutral Higgs and gauge bosons in the ditau final state produced in 36 fb-1 of pp collisions at √{s}=13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;... Franklin, M.;... Huth, J.;... Morii, M.;...
Publication:
Journal of High Energy Physics, Volume 2018, Issue 1, article id. #55, 54 pp.
Publication Date:
01/2018
Origin:
SPRINGER
Keywords:
Beyond Standard Model, Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2018: The Author(s)
DOI:
10.1007/JHEP01(2018)055
Bibliographic Code:
2018JHEP...01..055A

Abstract

A search for heavy neutral Higgs bosons and Z' bosons is performed using a data sample corresponding to an integrated luminosity of 36.1 fb-1 from proton-proton collisions at √{s}=13 TeV recorded by the ATLAS detector at the LHC during 2015 and 2016. The heavy resonance is assumed to decay to τ+ τ- with at least one tau lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-2.25 TeV for Higgs bosons and 0.2-4.0 TeV for Z' bosons. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in benchmark scenarios. In the context of the hMSSM scenario, the data exclude tan β > 1 .0 for m A = 0 .25 TeV and tan β > 42 for m A = 1 .5 TeV at the 95% confidence level. For the Sequential Standard Model, Z SSM ' with m Z' < 2.42 TeV is excluded at 95% confidence level, while Z NU ' with m Z ' < 2.25 TeV is excluded for the non-universal G(221) model that exhibits enhanced couplings to third-generation fermions. [Figure not available: see fulltext.]

 

Title:
Measurement of the cross-section for producing a W boson in association with a single top quark in pp collisions at √{s}=13 TeV with ATLAS
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; ... Franklin, M.;... Huth, J.;... Morii, M.;...
Publication:
Journal of High Energy Physics, Volume 2018, Issue 1, article id. #63, 42 pp.
Publication Date:
01/2018
Origin:
SPRINGER
Keywords:
Hadron-Hadron scattering (experiments)
Abstract Copyright:
(c) 2018: The Author(s)
DOI:
10.1007/JHEP01(2018)063
Bibliographic Code:
2018JHEP...01..063A

Abstract

The inclusive cross-section for the associated production of a W boson and top quark is measured using data from proton-proton collisions at √{s}=13 TeV. The dataset corresponds to an integrated luminosity of 3.2 fb-1, and was collected in 2015 by the ATLAS detector at the Large Hadron Collider at CERN. Events are selected requiring two opposite sign isolated leptons and at least one jet; they are separated into signal and control regions based on their jet multiplicity and the number of jets that are identified as containing b hadrons. The W t signal is then separated from the t\overline{t} background using boosted decision tree discriminants in two regions. The cross-section is extracted by fitting templates to the data distributions, and is measured to be σ W t = 94 ± 10(stat.) -22 +28 (syst.) ± 2(lumi.) pb. The measured value is in good agreement with the SM prediction of σ theory = 71 .7±1 .8 (scale)± 3 .4 (PDF) pb [1]. [Figure not available: see fulltext.]

 

Title:
Controlled Electrochemical Intercalation of Graphene/h-BN van der Waals Heterostructures
Authors:
Zhao, S. Y. Frank; Elbaz, Giselle A.; Bediako, D. Kwabena; Yu, Cyndia; Efetov, Dmitri K.; Guo, Yinsheng; Ravichandran, Jayakanth; Min, Kyung-Ah; Hong, Suklyun; Taniguchi, Takashi; Watanabe, Kenji; Brus, Louis E.; Roy, Xavier; Kim, Philip
Affiliation:
AE(0000-0001-5862-0462), AF(0000-0002-0571-8447), AL(0000-0002-5337-5776), AM(0000-0002-8850-0725), AN(0000-0002-8255-0086)
Publication:
Nano Letters, vol. 18, issue 1, pp. 460-466
Publication Date:
01/2018
Origin:
CROSSREF
DOI:
10.1021/acs.nanolett.7b04396
Bibliographic Code:
2018NanoL..18..460Z

Abstract

Electrochemical intercalation is a powerful method for tuning the electronic properties of layered solids. In this work, we report an electro-chemical strategy to controllably intercalate lithium ions into a series of van der Waals (vdW) heterostructures built by sandwiching graphene between hexagonal boron nitride (h-BN). We demonstrate that encapsulating graphene with h-BN eliminates parasitic surface side reactions while simultaneously creating a new hetero-interface that permits intercalation between the atomically thin layers. To monitor the electrochemical process, we employ the Hall effect to precisely monitor the intercalation reaction. We also simultaneously probe the spectroscopic and electrical transport properties of the resulting intercalation compounds at different stages of intercalation. We achieve the highest carrier density $> 5 \times 10^{13} cm^{-2}$ with mobility $> 10^3 cm^2/(Vs)$ in the most heavily intercalated samples, where Shubnikov-de Haas quantum oscillations are observed at low temperatures. These results set the stage for further studies that employ intercalation in modifying properties of vdW heterostructures.

 

Title:
Topological materials discovery using electron filling constraints
Authors:
Chen, Ru; Po, Hoi Chun; Neaton, Jeffrey B.; Vishwanath, Ashvin
Publication:
Nature Physics, Volume 14, Issue 1, pp. 55-61 (2018).
Publication Date:
01/2018
Origin:
NATURE
Abstract Copyright:
(c) 2018: Nature Publishing Group
DOI:
10.1038/nphys4277
Bibliographic Code:
2018NatPh..14...55C

Abstract

Nodal semimetals are classes of topological materials that have nodal-point or nodal-line Fermi surfaces, which give them novel transport and topological properties. Despite being highly sought after, there are currently very few experimental realizations, and identifying new materials candidates has mainly relied on exhaustive database searches. Here we show how recent studies on the interplay between electron filling and nonsymmorphic space-group symmetries can guide the search for filling-enforced nodal semimetals. We recast the previously derived constraints on the allowed band-insulator fillings in any space group into a new form, which enables effective screening of materials candidates based solely on their space group, electron count in the formula unit, and multiplicity of the formula unit. This criterion greatly reduces the computation load for discovering topological materials in a database of previously synthesized compounds. As a demonstration, we focus on a few selected nonsymmorphic space groups which are predicted to host filling-enforced Dirac semimetals. Of the more than 30,000 entires listed, our filling criterion alone eliminates 96% of the entries before they are passed on for further analysis. We discover a handful of candidates from this guided search; among them, the monoclinic crystal Ca2Pt2Ga is particularly promising.

 

Title:
Probing condensed matter physics with magnetometry based on nitrogen-vacancy centres in diamond
Authors:
Casola, Francesco; van der Sar, Toeno; Yacoby, Amir
Publication:
Nature Reviews Materials, Volume 3, Issue 1, pp. 17088 (2018).
Publication Date:
01/2018
Origin:
NATURE
Abstract Copyright:
(c) 2018: Macmillan Publishers Limited
DOI:
10.1038/natrevmats.2017.88
Bibliographic Code:
2018NatRM...317088C

Abstract

The magnetic fields generated by spins and currents provide a unique window into the physics of correlated-electron materials and devices. First proposed only a decade ago, magnetometry based on the electron spin of nitrogen-vacancy (NV) defects in diamond is emerging as a platform that is excellently suited for probing condensed matter systems; it can be operated from cryogenic temperatures to above room temperature, has a dynamic range spanning from direct current to gigahertz and allows sensor-sample distances as small as a few nanometres. As such, NV magnetometry provides access to static and dynamic magnetic and electronic phenomena with nanoscale spatial resolution. Pioneering work has focused on proof-of-principle demonstrations of its nanoscale imaging resolution and magnetic field sensitivity. Now, experiments are starting to probe the correlated-electron physics of magnets and superconductors and to explore the current distributions in low-dimensional materials. In this Review, we discuss the application of NV magnetometry to the exploration of condensed matter physics, focusing on its use to study static and dynamic magnetic textures and static and dynamic current distributions.

 

Title:
Bright nanowire single photon source based on SiV centers in diamond
Authors:
Marseglia, L.; Saha, K.; Ajoy, A.; Schröder, T.; Englund, D.; Jelezko, F.; Walsworth, R.; Pacheco, J. L.; Perry, D. L.; Bielejec, E. S.; Cappellaro, P.
Affiliation:
AK(0000-0003-3207-594X)
Publication:
Optics Express, vol. 26, issue 1, p. 80
Publication Date:
01/2018
Origin:
CROSSREF
DOI:
10.1364/OE.26.000080
Bibliographic Code:
2018OExpr..26...80M

Abstract

The practical implementation of many quantum technologies relies on the development of robust and bright single photon sources that operate at room temperature. The negatively charged silicon-vacancy (SiV-) color center in diamond is a possible candidate for such a single photon source. However, due to the high refraction index mismatch to air, color centers in diamond typically exhibit low photon out-coupling. An additional shortcoming is due to the random localization of native defects in the diamond sample. Here we demonstrate deterministic implantation of Si ions with high conversion efficiency to single SiV- centers, targeted to fabricated nanowires. The co-localization of single SiV- centers with the nanostructures yields a ten times higher light coupling efficiency than for single SiV- centers in bulk diamond. This enhanced photon out-coupling, together with the intrinsic scalability of the SiV- creation method, enables a new class of devices for integrated photonics and quantum science.

 

Title:
Measurement of differential cross sections of isolated-photon plus heavy-flavour jet production in pp collisions at √{ s } = 8 TeV using the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; ... Franklin, M.;... Huth, J.;... Morii, M.;...
Publication:
Physics Letters B, Volume 776, p. 295-317.
Publication Date:
01/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2017.11.054
Bibliographic Code:
2018PhLB..776..295A

Abstract

This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb-1. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: |ηγ | < 1.37 and 1.56 < |ηγ | < 2.37. The measurement covers photon transverse energies 25 < ETγ < 400 GeV and 25 < ETγ < 350 GeV respectively for the two |ηγ | regions. For each jet flavour, the ratio of the cross sections in the two |ηγ | regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central γ + b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.

 

Title:
Search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a Z boson in pp collisions at √{ s } = 13 TeV with the ATLAS detector
Authors:
Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.;
Publication:
Physics Letters B, Volume 776, p. 318-337.
Publication Date:
01/2018
Origin:
ELSEVIER
Abstract Copyright:
(c) 2018 Elsevier Science B.V. All rights reserved.
DOI:
10.1016/j.physletb.2017.11.049
Bibliographic Code:
2018PhLB..776..318A

Abstract

A search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying Z boson in proton-proton collisions at √{ s } = 13 TeV is presented. This search uses 36.1 fb-1 of data collected by the ATLAS experiment at the Large Hadron Collider. No significant deviation from the expectation of the Standard Model backgrounds is observed. Assuming the Standard Model ZH production cross-section, an observed (expected) upper limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of the Higgs boson with mass mH = 125 GeV. The corresponding limits on the production cross-section of the ZH process with the invisible Higgs boson decays are also presented. Furthermore, exclusion limits on the dark matter candidate and mediator masses are reported in the framework of simplified dark matter models.

 

Title:
Universal behavior of a dispersive Dirac cone in gradient-index plasmonic metamaterials
Authors:
Maier, Matthias; Mattheakis, Marios; Kaxiras, Efthimios; Luskin, Mitchell; Margetis, Dionisios
Publication:
Physical Review B, Volume 97, Issue 3, id.035307 (PhRvB Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevB.97.035307
Bibliographic Code:
2018PhRvB..97c5307M

Abstract

We demonstrate analytically and numerically that the dispersive Dirac cone emulating an epsilon-near-zero (ENZ) behavior is a universal property within a family of plasmonic crystals consisting of two-dimensional (2D) metals. Our starting point is a periodic array of 2D metallic sheets embedded in an inhomogeneous and anisotropic dielectric host that allows for propagation of transverse-magnetic (TM) polarized waves. By invoking a systematic bifurcation argument for arbitrary dielectric profiles in one spatial dimension, we show how TM Bloch waves experience an effective dielectric function that averages out microscopic details of the host medium. The corresponding effective dispersion relation reduces to a Dirac cone when the conductivity of the metallic sheet and the period of the array satisfy a critical condition for ENZ behavior. Our analytical findings are in excellent agreement with numerical simulations.

 

Title:
Power spectrum of dark matter substructure in strong gravitational lenses
Authors:
Diaz Rivero, Ana; Cyr-Racine, Francis-Yan; Dvorkin, Cora
Publication:
Physical Review D, Volume 97, Issue 2, id.023001 (PhRvD Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevD.97.023001
Bibliographic Code:
2018PhRvD..97b3001D

Abstract

Studying the smallest self-bound dark matter structure in our Universe can yield important clues about the fundamental particle nature of dark matter. Galaxy-scale strong gravitational lensing provides a unique way to detect and characterize dark matter substructures at cosmological distances from the Milky Way. Within the cold dark matter (CDM) paradigm, the number of low-mass subhalos within lens galaxies is expected to be large, implying that their contribution to the lensing convergence field is approximately Gaussian and could thus be described by their power spectrum. We develop here a general formalism to compute from first principles the substructure convergence power spectrum for different populations of dark matter subhalos. As an example, we apply our framework to two distinct subhalo populations: a truncated Navarro-Frenk-White subhalo population motivated by standard CDM, and a truncated cored subhalo population motivated by self-interacting dark matter (SIDM). We study in detail how the subhalo abundance, mass function, internal density profile, and concentration affect the amplitude and shape of the substructure power spectrum. We determine that the power spectrum is mostly sensitive to a specific combination of the subhalo abundance and moments of the mass function, as well as to the average tidal truncation scale of the largest subhalos included in the analysis. Interestingly, we show that the asymptotic slope of the substructure power spectrum at large wave number reflects the internal density profile of the subhalos. In particular, the SIDM power spectrum exhibits a characteristic steepening at large wave number absent in the CDM power spectrum, opening the possibility of using this observable, if at all measurable, to discern between these two scenarios.

 

Title:
Surfactant Variations in Porous Media Localize Capillary Instabilities during Haines Jumps
Authors:
Edery, Yaniv; Weitz, David; Berg, Steffen
Publication:
Physical Review Letters, Volume 120, Issue 2, id.028005 (PhRvL Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevLett.120.028005
Bibliographic Code:
2018PhRvL.120b8005E

Abstract

We use confocal microscopy to measure velocity and interfacial tension between a trapped wetting phase with a surfactant and a flowing, invading nonwetting phase in a porous medium. We relate interfacial tension variations at the fluid-fluid interface to surfactant concentration and show that these variations localize the destabilization of capillary forces and lead to rapid local invasion of the nonwetting fluid, resulting in a Haines jump. These spatial variations in surfactant concentration are caused by velocity variations at the fluid-fluid interfaces and lead to localization of the Haines jumps even in otherwise very uniform pore structure and pressure conditions. Our results provide new insight into the nature of Haines jumps, one of the most ubiquitous and important instabilities in flow in porous media.

 

Title:
Large Excitonic Reflectivity of Monolayer MoSe2 Encapsulated in Hexagonal Boron Nitride
Authors:
Scuri, Giovanni; Zhou, You; High, Alexander A.; Wild, Dominik S.; Shu, Chi; De Greve, Kristiaan; Jauregui, Luis A.; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip; Lukin, Mikhail D.; Park, Hongkun
Publication:
Physical Review Letters, Volume 120, Issue 3, id.037402 (PhRvL Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/PhysRevLett.120.037402
Bibliographic Code:
2018PhRvL.120c7402S

Abstract

We demonstrate that a single layer of MoSe2 encapsulated by hexagonal boron nitride can act as an electrically switchable mirror at cryogenic temperatures, reflecting up to 85% of incident light at the excitonic resonance. This high reflectance is a direct consequence of the excellent coherence properties of excitons in this atomically thin semiconductor. We show that the MoSe2 monolayer exhibits power-and wavelength-dependent nonlinearities that stem from exciton-based lattice heating in the case of continuous-wave excitation and exciton-exciton interactions when fast, pulsed laser excitation is used.

 

Title:
Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron
Authors:
Aaltonen, T.; Abazov, V. M.; Abbott, B.;... Franklin, M.;... CDF Collaboration
Publication:
Physical Review Letters, Volume 120, Issue 4, id.042001 (PhRvL Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: authors
DOI:
10.1103/PhysRevLett.120.042001
Bibliographic Code:
2018PhRvL.120d2001A

Abstract

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of √{s }=1.96 TeV . We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is AFBtt ¯=0.128 ±0.025 . The combined inclusive and differential asymmetries are consistent with recent standard model predictions.

 

Title:
Fermionic Spinon Theory of Square Lattice Spin Liquids near the Néel State
Authors:
Thomson, Alex; Sachdev, Subir
Publication:
Physical Review X, Volume 8, Issue 1, id.011012
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: authors
DOI:
10.1103/PhysRevX.8.011012
Bibliographic Code:
2018PhRvX...8a1012T

Abstract

Quantum fluctuations of the Néel state of the square lattice antiferromagnet are usually described by a CP1 theory of bosonic spinons coupled to a U(1) gauge field, and with a global SU(2) spin rotation symmetry. Such a theory also has a confining phase with valence bond solid (VBS) order, and upon including spin-singlet charge-2 Higgs fields, deconfined phases with Z2 topological order possibly intertwined with discrete broken global symmetries. We present dual theories of the same phases starting from a mean-field theory of fermionic spinons moving in π flux in each square lattice plaquette. Fluctuations about this π -flux state are described by (2 +1 )-dimensional quantum chromodynamics (QCD3 ) with a SU(2) gauge group and Nf=2 flavors of massless Dirac fermions. It has recently been argued by Wang et al. [Deconfined Quantum Critical Points: Symmetries and Dualities, Phys. Rev. X 7, 031051 (2017)., 10.1103/PhysRevX.7.031051] that this QCD3 theory describes the Néel-VBS quantum phase transition. We introduce adjoint Higgs fields in QCD3 and obtain fermionic dual descriptions of the phases with Z2 topological order obtained earlier using the bosonic CP1 theory. We also present a fermionic spinon derivation of the monopole Berry phases in the U(1) gauge theory of the VBS state. The global phase diagram of these phases contains multicritical points, and our results imply new boson-fermion dualities between critical gauge theories of these points.

 

Title:
Silvan Samuel Schweber
Authors:
Galison, Peter; Kaiser, David
Publication:
Physics Today, vol. 71, issue 1, pp. 63-64
Publication Date:
01/2018
Origin:
CROSSREF
DOI:
10.1063/PT.3.3827
Bibliographic Code:
2018PhT....71a..63G

Abstract

Not Available

 

Title:
Weyl and Dirac semimetals in three-dimensional solids
Authors:
Armitage, N. P.; Mele, E. J.; Vishwanath, Ashvin
Publication:
Reviews of Modern Physics, Volume 90, Issue 1, id.015001 (RvMP Homepage)
Publication Date:
01/2018
Origin:
APS
Abstract Copyright:
2018: American Physical Society
DOI:
10.1103/RevModPhys.90.015001
Bibliographic Code:
2018RvMP...90a5001A

Abstract

Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.


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