Faculty Publications: March, 2015

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)

The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which appeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.

see also:
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Jan 2015 | Feb 2015

Title:
Stress controls the mechanics of collagen networks
Authors:
Licup, Albert James; Münster, Stefan; Sharma, Abhinav; Sheinman, Michael; Jawerth, Louise M.; Fabry, Ben; Weitz, David A.; MacKintosh, Fred C.
Publication:
eprint arXiv:1503.00924
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Comment:
manuscript: 8 pages, 3 figures, supporting information: 4 pages, 6 figures
Bibliographic Code:
2015arXiv150300924L

Abstract

Collagen is the main structural and load-bearing element of various connective tissues, where it forms the extracellular matrix that supports cells. It has long been known that collagenous tissues exhibit a highly nonlinear stress-strain relationship (Fung YC, Am J Physiol 213(6),1967; Humphrey JD, Proc R Soc Lond A: Math Phys Eng Sci 459(2029),2003), although the origins of this nonlinearity remain unknown (McMahon TA, Lec Math Life Sci 13,1980). Here, we show that the nonlinear stiffening of reconstituted type I collagen networks is controlled by the applied stress, and that the network stiffness becomes surprisingly insensitive to network concentration. We demonstrate how a simple model for networks of elastic fibers can quantitatively account for the mechanics of reconstituted collagen networks. Our model points to the important role of normal stresses in determining the nonlinear shear elastic response, which can explain the approximate exponential relationship between stress and strain reported for collagenous tissues (Fung YC, Am J Physiol 213(6),1967). This further suggests new principles for the design of synthetic fiber networks with collagen-like properties, as well as a mechanism for the control of the mechanics of such networks.

 

Title:
Solid friction between soft filaments
Authors:
Ward, Andrew; Hilitski, Feodor; Schwenger, Walter; Welch, David; Lau, A. W. C.; Vitelli, Vincenzo; Mahadevan, L.; Dogic, Zvonimir
Publication:
eprint arXiv:1503.01202
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
Physics - Biological Physics, Condensed Matter - Soft Condensed Matter, Quantitative Biology - Subcellular Processes
Comment:
doi:10.1038/nmat4222
Bibliographic Code:
2015arXiv150301202W

Abstract

Any macroscopic deformation of a filamentous bundle is necessarily accompanied by local sliding and/or stretching of the constituent filaments. Yet the nature of the sliding friction between two aligned filaments interacting through multiple contacts remains largely unexplored. Here, by directly measuring the sliding forces between two bundled F-actin filaments, we show that these frictional forces are unexpectedly large, scale logarithmically with sliding velocity as in solid-like friction, and exhibit complex dependence on the filaments' overlap length. We also show that a reduction of the frictional force by orders of magnitude, associated with a transition from solid-like friction to Stokes' drag, can be induced by coating F-actin with polymeric brushes. Furthermore, we observe similar transitions in filamentous microtubules and bacterial flagella. Our findings demonstrate how altering a filament's elasticity, structure and interactions can be used to engineer interfilament friction and thus tune the properties of fibrous composite materials.

 

Title:
On Higher Derivative Couplings in Theories with Sixteen Supersymmetries
Authors:
Lin, Ying-Hsuan; Shao, Shu-Heng; Wang, Yifan; Yin, Xi
Publication:
eprint arXiv:1503.02077
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
27 pages, 10 figures
Bibliographic Code:
2015arXiv150302077L

Abstract

We give simple arguments for new non-renormalization theorems on higher derivative couplings of gauge theories to supergravity, with sixteen supersymmetries, by considerations of brane-bulk superamplitudes. This leads to some exact results on the effective coupling of D3-branes in type IIB string theory. We also derive exact results on higher dimensional operators in the torus compactification of the six dimensional (0, 2) superconformal theory.

 

Title:
2D Kac-Moody Symmetry of 4D Yang-Mills Theory
Authors:
He, Temple; Mitra, Prahar; Strominger, Andrew
Publication:
eprint arXiv:1503.02663
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, High Energy Physics - Phenomenology
Comment:
18 pages
Bibliographic Code:
2015arXiv150302663H

Abstract

Scattering amplitudes of any four-dimensional theory with nonabelian gauge group $\mathcal G$ may be recast as two-dimensional correlation functions on the asymptotic two-sphere at null infinity. The soft gluon theorem is shown, for massless theories at the semiclassical level, to be the Ward identity of a holomorphic two-dimensional $\mathcal G$-Kac-Moody symmetry acting on these correlation functions. Holomorphic Kac-Moody current insertions are positive helicity soft gluon insertions. The Kac-Moody transformations are a $CPT$ invariant subgroup of gauge transformations which act nontrivially at null infinity and comprise the four-dimensional asymptotic symmetry group.

 

Title:
Revealing the Empty-State Electronic Structure of Single-Unit-Cell FeSe/SrTiO$_{3}$
Authors:
Huang, Dennis; Song, Can-Li; Webb, Tatiana A.; Fang, Shiang; Chang, Cui-Zu; Moodera, Jagadeesh S.; Kaxiras, Efthimios; Hoffman, Jennifer E.
Publication:
eprint arXiv:1503.04792
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Comment:
5 pages, 5 figures
Bibliographic Code:
2015arXiv150304792H

Abstract

We use scanning tunneling spectroscopy to investigate the filled and empty electronic states of superconducting single-unit-cell FeSe deposited on SrTiO$_3$(001). We map the momentum-space band structure by combining quasiparticle interference imaging with decay length spectroscopy. In addition to quantifying the filled-state bands, we discover a $\Gamma$-centered electron pocket 75 meV above the Fermi energy. Our density functional theory calculations show the orbital nature of empty states at $\Gamma$ and suggest that the Se height is a key tuning parameter of their energies, with broad implications for electronic properties.

 

Title:
Spectral weight redistribution in (LaNiO3)n/(LaMnO3)2 superlattices from optical spectroscopy
Authors:
Di Pietro, P.; Hoffman, J.; Bhattacharya, A.; Lupi, S.; Perucchi, A.
Publication:
eprint arXiv:1503.07328
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons
Comment:
Accepted for publication in Phys. Rev. Lett. 5 pages, 5 figures
Bibliographic Code:
2015arXiv150307328D

Abstract

We have studied the optical properties of four (LaNiO$_3$)$_n$/(LaMnO$_3$)$_2$ superlattices (SL) ($n$=2, 3, 4, 5) on SrTiO$_3$ substrates. We have measured the reflectivity at temperatures from 20 K to 400 K, and extracted the optical conductivity through a fitting procedure based on a Kramers-Kronig consistent Lorentz-Drude model. With increasing LaNiO$_3$ thickness, the SLs undergo an insulator-to-metal transition (IMT) that is accompanied by the transfer of spectral weight from high to low frequency. The presence of a broad mid-infrared band, however, shows that the optical conductivity of the (LaNiO$_3$)$_n$/(LaMnO$_3$)$_2$ SLs is not a linear combination of the LaMnO$_3$ and LaNiO$_3$ conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites.

 

Title:
Adiabatic Isometric Mapping Algorithm for Embedding 2-Surfaces in Euclidean 3-Space
Authors:
Ray, Shannon; Miller, Warner A.; Alsing, Paul M.; Yau, Shing-Tung
Publication:
eprint arXiv:1503.07556
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
General Relativity and Quantum Cosmology
Bibliographic Code:
2015arXiv150307556R

Abstract

Alexandrov proved that any simplicial complex homeomorphic to a sphere with strictly non-negative Gaussian curvature at each vertex can be isometrically embedded uniquely in $\mathbb{R}^3$ as a convex polyhedron. Due to the nonconstructive nature of his proof, there have yet to be any algorithms, that we know of, that realizes the Alexandrov embedding in polynomial time. Following his proof, we developed the adiabatic isometric mapping (AIM) algorithm. AIM uses a guided adiabatic pull-back procedure to produce "smooth" embeddings. Tests of AIM applied to two different polyhedral metrics suggests that its run time is sub cubic with respect to the number of vertices. Although Alexandrov's theorem specifically addresses the embedding of convex polyhedral metrics, we tested AIM on a broader class of polyhedral metrics that included regions of negative Gaussian curvature. One test was on a surface just outside the ergosphere of a Kerr black hole.

 

Title:
Observation of seasonal variation of atmospheric multiple-muon events in the MINOS Near and Far Detectors
Authors:
Adamson, P.; Anghel, I.; Aurisano, A.;... Feldman, G. J.;... and 106 coauthors
Publication:
eprint arXiv:1503.09104
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Experiment
Bibliographic Code:
2015arXiv150309104A

Abstract

We report the first observation of seasonal modulations in the rates of cosmic ray multiple-muon events at two underground sites, the MINOS Near Detector with an overburden of 225 mwe, and the MINOS Far Detector site at 2100 mwe. At the deeper site, multiple-muon events with muons separated by more than 8 m exhibit a seasonal rate that peaks during the summer, similar to that of single-muon events. In contrast and unexpectedly, the rate of multiple-muon events with muons separated by less than 5-8 m, and the rate of multiple-muon events in the smaller, shallower Near Detector, exhibit a seasonal rate modulation that peaks in the winter.

 

Title:
Conformal Surface Morphing with Applications on Facial Expressions
Authors:
Yueh, Mei-Heng; Gu, Xianfeng David; Lin, Wen-Wei; Wu, Chin-Tien; Yau, Shing-Tung
Publication:
eprint arXiv:1504.00097
Publication Date:
03/2015
Origin:
ARXIV
Keywords:
Computer Science - Graphics, Computer Science - Computational Geometry
Comment:
8 pages, 13 figures
Bibliographic Code:
2015arXiv150400097Y

Abstract

Morphing is the process of changing one figure into another. Some numerical methods of 3D surface morphing by deformable modeling and conformal mapping are shown in this study. It is well known that there exists a unique Riemann conformal mapping from a simply connected surface into a unit disk by the Riemann mapping theorem. The dilation and relative orientations of the 3D surfaces can be linked through the M\"obius transformation due to the conformal characteristic of the Riemann mapping. On the other hand, a 3D surface deformable model can be built via various approaches such as mutual parameterization from direct interpolation or surface matching using landmarks. In this paper, we take the advantage of the unique representation of 3D surfaces by the mean curvatures and the conformal factors associated with the Riemann mapping. By registering the landmarks on the conformal parametric domains, the correspondence of the mean curvatures and the conformal factors for each surfaces can be obtained. As a result, we can construct the 3D deformation field from the surface reconstruction algorithm proposed by Gu and Yau. Furthermore, by composition of the M\"obius transformation and the 3D deformation field, the morphing sequence can be generated from the mean curvatures and the conformal factors on a unified mesh structure by using the cubic spline homotopy. Several numerical experiments of the face morphing are presented to demonstrate the robustness of our approach.

 

Title:
Switching of Bacterial Flagellar Motors Is Triggered by Mutant FliG
Authors:
Lele, Pushkar P.; Berg, Howard C.
Publication:
Biophysical Journal, vol. 108, issue 5, pp. 1275-1280
Publication Date:
03/2015
Origin:
CROSSREF
DOI:
10.1016/j.bpj.2015.02.004
Bibliographic Code:
2015BpJ...108.1275L

Abstract

Not Available

 

Title:
M-Strings
Authors:
Haghighat, Babak; Iqbal, Amer; Kozçaz, Can; Lockhart, Guglielmo; Vafa, Cumrun
Publication:
Communications in Mathematical Physics, Volume 334, Issue 2, pp.779-842
Publication Date:
03/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: Springer-Verlag Berlin Heidelberg
DOI:
10.1007/s00220-014-2139-1
Bibliographic Code:
2015CMaPh.334..779H

Abstract

M2 branes suspended between adjacent parallel M5 branes lead to light strings, the `M-strings'. In this paper we compute the elliptic genus of M-strings, twisted by maximally allowed symmetries that preserve 2 d (2, 0) supersymmetry. In a codimension one subspace of parameters this reduces to the elliptic genus of the (4, 4) supersymmetric A n-1 quiver theory in 2 d. We contrast the elliptic genus of N M-strings with the (4, 4) sigma model on the N-fold symmetric product of . For N = 1 they are the same, but for N > 1 they are close, but not identical. Instead the elliptic genus of (4, 4) N M-strings is the same as the elliptic genus of (4, 0) sigma models on the N-fold symmetric product of , but where the right-moving fermions couple to a modification of the tangent bundle. This construction arises from a dual A n-1 quiver 6 d gauge theory with U(1) gauge groups. Moreover, we compute the elliptic genus of domain walls which separate different numbers of M2 branes on the two sides of the wall.

 

Title:
Performance of the ATLAS muon trigger in pp collisions at TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2890 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #120, 31 pp. (EPJC Homepage)
Publication Date:
03/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-015-3325-9
Bibliographic Code:
2015EPJC...75..120A

Abstract

The performance of the ATLAS muon trigger system is evaluated with proton-proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum GeV, with a statistical uncertainty of less than 0.01 % and a systematic uncertainty of 0.6 %. The range for efficiency determination is extended by using muons from decays of mesons, bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.

 

Title:
Femtosecond-laser hyperdoping silicon in an SF6 atmosphere: Dopant incorporation mechanism
Authors:
Sher, Meng-Ju; Mangan, Niall M.; Smith, Matthew J.; Lin, Yu-Ting; Marbach, Sophie; Schneider, Tobias M.; Gradecak, Silvija; Brenner, Michael P.; Mazur, Eric
Publication:
Journal of Applied Physics, Volume 117, Issue 12, id.125301 (JAP Homepage)
Publication Date:
03/2015
Origin:
AIP
Abstract Copyright:
2015: AIP Publishing LLC
DOI:
10.1063/1.4914520
Bibliographic Code:
2015JAP...117l5301S

Abstract

In this paper, we examine the fundamental processes that occur during femtosecond-laser hyperdoping of silicon with a gas-phase dopant precursor. We probe the dopant concentration profile as a function of the number of laser pulses and pressure of the dopant precursor (sulfur hexafluoride). In contrast to previous studies, we show the hyperdoped layer is single crystalline. From the dose dependence on pressure, we conclude that surface adsorbed molecules are the dominant source of the dopant atoms. Using numerical simulation, we estimate the change in flux with increasing number of laser pulses to fit the concentration profiles. We hypothesize that the native oxide plays an important role in setting the surface boundary condition. As a result of the removal of the native oxide by successive laser pulses, dopant incorporation is more efficient during the later stage of laser irradiation.

 

Title:
Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with TeV pp collisions using the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2885 coauthors
Publication:
Journal of High Energy Physics, Volume 2015, article id. #41, 48 pp.
Publication Date:
03/2015
Origin:
SPRINGER
Keywords:
Hadron-Hadron Scattering, Beyond Standard Model, Particle and resonance production
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP03(2015)041
Bibliographic Code:
2015JHEP...03..041A

Abstract

A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb-1 of integrated luminosity taken in 2012 at a centre-of-mass energy of 8 TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e± e±, e± mu±, and mu± mu± are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production. [Figure not available: see fulltext.]

 

Title:
Employing confinement induced resonances to realize Kondo physics with ultracold atoms
Authors:
Bauer, J.; Demler, E.; Salomon, C.
Publication:
Journal of Physics: Conference Series, Volume 592, Issue 1, article id. 012151 (2015).
Publication Date:
03/2015
Origin:
IOP
DOI:
10.1088/1742-6596/592/1/012151
Bibliographic Code:
2015JPhCS.592a2151B

Abstract

We recently proposed a novel realization of Kondo physics with ultracold atomic gases and illustrated that a mixture of 40K and 23Na atoms has suitable properties for the generation of a Kondo-correlated state with experimentally accessible scales. This system fortuitously satisfies rather special conditions. Here we discuss an alternative realization based on confinement induced resonances which could also be applicable for other mixtures. We first explain the general principle of how to engineer the Kondo correlated state like this. Then we present results for local spectral functions from numerical renormalization group (NRG) calculations for the appropriate effective Anderson impurity model and also predict the experimentally measurable radio frequency response.

 

Title:
Control of Emergent Properties at a Correlated Oxide Interface with Graphene
Authors:
Zhou, You; Park, Jungwon; Shi, Jian; Chhowalla, Manish; Park, Hyesung; Weitz, David A.; Ramanathan, Shriram
Publication:
Nano Letters, vol. 15, issue 3, pp. 1627-1634
Publication Date:
03/2015
Origin:
CROSSREF
DOI:
10.1021/nl504170d
Bibliographic Code:
2015NanoL..15.1627Z

Abstract

Not Available

 

Title:
One-step direct-laser metal writing of sub-100 nm 3D silver nanostructures in a gelatin matrix
Authors:
Kang, SeungYeon; Vora, Kevin; Mazur, Eric
Publication:
Nanotechnology, Volume 26, Issue 12, article id. 121001 (2015).
Publication Date:
03/2015
Origin:
IOP
DOI:
10.1088/0957-4484/26/12/121001
Bibliographic Code:
2015Nanot..26l1001K

Abstract

Developing an ability to fabricate high-resolution, 3D metal nanostructures in a stretchable 3D matrix is a critical step to realizing novel optoelectronic devices such as tunable bulk metal-dielectric optical devices and THz metamaterial devices that are not feasible with alternative techniques. We report a new chemistry method to fabricate high-resolution, 3D silver nanostructures using a femtosecond-laser direct metal writing technique. Previously, only fabrication of 3D polymeric structures or single-/few-layer metal structures was possible. Our method takes advantage of unique gelatin properties to overcome such previous limitations as limited freedom in 3D material design and short sample lifetime. We fabricate more than 15 layers of 3D silver nanostructures with a resolution of less than 100 nm in a stable dielectric matrix that is flexible and has high large transparency that is well-matched for potential applications in the optical and THz metamaterial regimes. This is a single-step process that does not require any further processing. This work will be of interest to those interested in fabrication methods that utilize nonlinear light--matter interactions and the realization of future metamaterials.

 

Title:
Oscillation of the velvet worm slime jet by passive hydrodynamic instability
Authors:
Concha, Andrés; Mellado, Paula; Morera-Brenes, Bernal; Sampaio Costa, Cristiano; Mahadevan, L.; Monge-Nájera, Julián
Publication:
Nature Communications, Volume 6, id. 6292 (2015).
Publication Date:
03/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.
DOI:
10.1038/ncomms7292
Bibliographic Code:
2015NatCo...6E6292C

Abstract

The rapid squirt of a proteinaceous slime jet endows velvet worms (Onychophora) with a unique mechanism for defence from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date, neither qualitative nor quantitative descriptions have been provided for this unique adaptation. Here we investigate the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with frequencies f~30--60 Hz. Using anatomical images, high-speed videography, theoretical analysis and a physical simulacrum, we show that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Our results demonstrate how passive strategies can be cleverly harnessed by organisms, while suggesting future oscillating microfluidic devices, as well as novel ways for micro and nanofibre production using bioinspired strategies.

 

Title:
Confinement-induced interlayer molecules: A route to strong interatomic interactions
Authors:
Kanász-Nagy, M.; Demler, E. A.; Zaránd, G.
Publication:
Physical Review A, Volume 91, Issue 3, id.032704 (PhRvA Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Scattering of atoms and molecules, Ultracold gases trapped gases
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevA.91.032704
Bibliographic Code:
2015PhRvA..91c2704K

Abstract

We study theoretically the interaction between two species of ultracold atoms confined in two layers of a finite separation and demonstrate the existence of confinement-induced interlayer bound and quasibound molecules: These excitonlike interlayer molecules appear for both positive and negative scattering lengths and exist even for layer separations many times larger than the interspecies scattering length. The lifetime of the quasibound molecules grows exponentially with increasing layer separation and the molecules can therefore be observed in simple shaking experiments, as we demonstrate through detailed many-body calculations. These quasibound molecules can also give rise to interspecies Feshbach resonances, enabling one to control geometrically the interaction between the two species by changing the layer separation. Rather counterintuitively, the species can be made strongly interacting, by actually increasing their spatial separation. The separation-induced interlayer resonances provide a powerful tool for the experimental control of interspecies interactions and enables one to realize novel quantum phases of multicomponent quantum gases.

 

Title:
Cooper pairing in non-Fermi liquids
Authors:
Metlitski, Max A.; Mross, David F.; Sachdev, Subir; Senthil, T.
Publication:
Physical Review B, Volume 91, Issue 11, id.115111 (PhRvB Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems, Quantum phase transitions
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.115111
Bibliographic Code:
2015PhRvB..91k5111M

Abstract

States of matter with a sharp Fermi surface but no well-defined Landau quasiparticles arise in a number of physical systems. Examples include (i) quantum critical points associated with the onset of order in metals; (ii) spinon Fermi-surface [U(1) spin-liquid] state of a Mott insulator; (iii) Halperin-Lee-Read composite fermion charge liquid state of a half-filled Landau level. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi liquids in two spatial dimensions to Cooper pairing. We consider the Ising-nematic quantum critical point as an example of an ordering phase transition in a metal, and demonstrate that the attractive interaction mediated by the order-parameter fluctuations always leads to a superconducting instability. Moreover, in the regime where our calculation is controlled, superconductivity preempts the destruction of electronic quasiparticles. On the other hand, the spinon Fermi surface and the Halperin-Lee-Read states are stable against Cooper pairing for a sufficiently weak attractive short-range interaction; however, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between (i) U(1 ) and Z2 spin-liquid states; (ii) Halperin-Lee-Read and Moore-Read states.

 

Title:
Higgs criticality in a two-dimensional metal
Authors:
Chowdhury, Debanjan; Sachdev, Subir
Publication:
Physical Review B, Volume 91, Issue 11, id.115123 (PhRvB Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Non-Fermi-liquid ground states electron phase diagrams and phase transitions in model systems
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.115123
Bibliographic Code:
2015PhRvB..91k5123C

Abstract

We analyze a candidate theory for the strange metal near optimal hole doping in the cuprate superconductors. The theory contains a quantum phase transition between metals with large and small Fermi surfaces of spinless fermions carrying the electromagnetic charge of the electron, but the transition does not directly involve any broken global symmetries. The two metals have emergent SU(2) and U(1) gauge fields respectively, and the transition is driven by the condensation of a real Higgs field, carrying a finite lattice momentum and an adjoint SU(2) gauge charge. This Higgs field measures the local antiferromagnetic correlations in a "rotating reference frame." We propose a global phase diagram around this Higgs transition, and describe its relationship to a variety of recent experiments on the cuprate superconductors.

 

Title:
Simultaneous measurements of the t t ¯, W+W-, and Z /gamma*-->tau tau production cross-sections in p p collisions at &surd;{s }=7 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2890 coauthors
Publication:
Physical Review D, Volume 91, Issue 5, id.052005 (PhRvD Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Total cross sections, Top quarks, W bosons, Z bosons
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.052005
Bibliographic Code:
2015PhRvD..91e2005A

Abstract

Simultaneous measurements of the t t ¯, W+W-, and Z /gamma*-->tau tau production cross-sections using an integrated luminosity of 4.6 fb-1 of p p collisions at &surd;{s }=7 TeV collected by the ATLAS detector at the LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. These results indicate that the correlated next-to-leading-order predictions for t t ¯ and Z /gamma*-->tau tau underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be sigma (t t ¯ )=181.2 ±2. 8-9.5+9.7±3.3 ±3.3 pb, sigma (W+W-)=53.3 ±2. 7-8.0+7.3±1.0 ±0.5 pb, and sigma (Z /gamma*-->tau tau )=1174 ±2 4-87+72±21 ±9 pb , where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W+W- measurement includes the small contribution from Higgs boson decays, H -->W+W-.

 

Title:
Search for new phenomena in the dijet mass distribution using p p collision data at &surd;{s }=8 TeV with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... ; Huth, J.;... Morii, M.;... and 2885 coauthors
Publication:
Physical Review D, Volume 91, Issue 5, id.052007 (PhRvD Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Composite models, Production, Other particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.052007
Bibliographic Code:
2015PhRvD..91e2007A

Abstract

Dijet events produced in LHC proton-proton collisions at a center-of-mass energy &surd;{s }=8 TeV are studied with the ATLAS detector using the full 2012 data set, with an integrated luminosity of 20.3 fb-1 . Dijet masses up to about 4.5 TeV are probed. No resonancelike features are observed in the dijet mass spectrum. Limits on the cross section times acceptance are set at the 95% credibility level for various hypotheses of new phenomena in terms of mass or energy scale, as appropriate. This analysis excludes excited quarks with a mass below 4.06 TeV, color-octet scalars with a mass below 2.70 TeV, heavy W' bosons with a mass below 2.45 TeV, chiral W* bosons with a mass below 1.75 TeV, and quantum black holes with six extra space-time dimensions with threshold mass below 5.66 TeV.

 

Title:
Search for production of an Upsilon (1 S ) meson in association with a W or Z boson using the full 1.96 TeV p p ¯ collision data set at CDF
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 398 coauthors
Publication:
Physical Review D, Volume 91, Issue 5, id.052011 (PhRvD Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Gauge bosons, Nonrelativistic quark model
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.052011
Bibliographic Code:
2015PhRvD..91e2011A

Abstract

Production of the Upsilon (1 S ) meson in association with a vector boson is a rare process in the standard model with a cross section predicted to be below the sensitivity of the Tevatron. Observation of this process could signify contributions not described by the standard model or reveal limitations with the current nonrelativistic quantum-chromodynamic models used to calculate the cross section. We perform a search for this process using the full Run II data set collected by the CDF II detector corresponding to an integrated luminosity of 9.4 fb-1 . The search considers the Upsilon -->mu mu decay and the decay of the W and Z bosons into muons and electrons. In these purely leptonic decay channels, we observe one Upsilon W candidate with an expected background of 1.2 ±0.5 events, and one Upsilon Z candidate with an expected background of 0.1 ±0.1 events. Both observations are consistent with the predicted background contributions. The resulting upper limits on the cross section for Upsilon +W /Z production are the most sensitive reported from a single experiment and place restrictions on potential contributions from non-standard-model physics.

 

Title:
Crystallization and reentrant melting of charged colloids in nonpolar solvents
Authors:
Kanai, Toshimitsu; Boon, Niels; Lu, Peter J.; Sloutskin, Eli; Schofield, Andrew B.; Smallenburg, Frank; van Roij, René; Dijkstra, Marjolein; Weitz, David A.
Publication:
Physical Review E, Volume 91, Issue 3, id.030301 (PhRvE Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Colloids, Crystallographic aspects of phase transformations, pressure effects, Order-disorder transformations, statistical mechanics of model systems, Colloids
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevE.91.030301
Bibliographic Code:
2015PhRvE..91c0301K

Abstract

We explore the crystallization of charged colloidal particles in a nonpolar solvent mixture. We simultaneously charge the particles and add counterions to the solution with aerosol-OT (AOT) reverse micelles. At low AOT concentrations, the charged particles crystallize into body-centered-cubic (bcc) or face-centered-cubic (fcc) Wigner crystals; at high AOT concentrations, the increased screening drives a thus far unobserved reentrant melting transition. We observe an unexpected scaling of the data with particle size, and account for all behavior with a model that quantitatively predicts both the reentrant melting and the data collapse.

 

Title:
Anisotropic elasticity of experimental colloidal Wigner crystals
Authors:
Russell, Emily R.; Spaepen, Frans; Weitz, David A.
Publication:
Physical Review E, Volume 91, Issue 3, id.032310 (PhRvE Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Colloids, Elastic moduli
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevE.91.032310
Bibliographic Code:
2015PhRvE..91c2310R

Abstract

Colloidal particles interacting via a long-range repulsion can, in contrast to hard-sphere systems, exhibit crystalline ordering at low volume fraction. Here we experimentally investigate the structure and properties of such "colloidal Wigner crystals." We find a body-centered-cubic crystalline phase at volume fractions of varphi ≳15 % , which exhibits large fluctuations of individual particles from their average positions. We determine the three independent crystalline elastic constants and find that these crystals are very compliant and highly anisotropic.

 

Title:
Joint Analysis of BICEP 2 /K e c k A r r a y and Planck Data
Authors:
Ade, P. A. R.; Aghanim, N.; Ahmed, Z.;... Kovac, J. M.;... and 268 coauthors; Bicep2/Keck; Planck Collaborations
Publication:
Physical Review Letters, Volume 114, Issue 10, id.101301 (PhRvL Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Background radiations, Gravitational wave detectors and experiments, Radio microwave, Observational cosmology
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.101301
Bibliographic Code:
2015PhRvL.114j1301A

Abstract

We report the results of a joint analysis of data from BICEP 2 /K e c k A r r a y and Planck. BICEP2 and Keck Array have observed the same approximately 400 deg2 patch of sky centered on RA 0 h, Dec. -57.5 ° . The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region (1.2 mu K deg in Q and U at 143 GHz). We detect 150 ×353 cross-correlation in B modes at high significance. We fit the single- and cross-frequency power spectra at frequencies >=150 GHz to a lensed-Lambda CDM model that includes dust and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio r ), using a prior on the frequency spectral behavior of polarized dust emission from previous Planck analysis of other regions of the sky. We find strong evidence for dust and no statistically significant evidence for tensor modes. We probe various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and find that these make little difference to the r constraint. Finally, we present an alternative analysis which is similar to a map-based cleaning of the dust contribution, and show that this gives similar constraints. The final result is expressed as a likelihood curve for r , and yields an upper limit r0.05 <0.12 at 95% confidence. Marginalizing over dust and r , lensing B modes are detected at 7.0 sigma significance.

 

Title:
Identifying Structural Flow Defects in Disordered Solids Using Machine-Learning Methods
Authors:
Cubuk, E. D.; Schoenholz, S. S.; Rieser, J. M.; Malone, B. D.; Rottler, J.; Durian, D. J.; Kaxiras, E.; Liu, A. J.
Publication:
Physical Review Letters, Volume 114, Issue 10, id.108001 (PhRvL Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Granular systems, Disordered solids, Deformation and plasticity, Deformation and flow
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.108001
Bibliographic Code:
2015PhRvL.114j8001C

Abstract

We use machine-learning methods on local structure to identify flow defects---or particles susceptible to rearrangement---in jammed and glassy systems. We apply this method successfully to two very different systems: a two-dimensional experimental realization of a granular pillar under compression and a Lennard-Jones glass in both two and three dimensions above and below its glass transition temperature. We also identify characteristics of flow defects that differentiate them from the rest of the sample. Our results show it is possible to discern subtle structural features responsible for heterogeneous dynamics observed across a broad range of disordered materials.

 

Title:
Heralded Quantum Gates with Integrated Error Detection in Optical Cavities
Authors:
Borregaard, J.; Kómár, P.; Kessler, E. M.; Sørensen, A. S.; Lukin, M. D.
Publication:
Physical Review Letters, Volume 114, Issue 11, id.110502 (PhRvL Homepage)
Publication Date:
03/2015
Origin:
APS
PACS Keywords:
Quantum computation, Quantum error correction and other methods for protection against decoherence, Coherent control of atomic interactions with photons, Optical implementations of quantum information processing and transfer
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.110502
Bibliographic Code:
2015PhRvL.114k0502B

Abstract

We propose and analyze heralded quantum gates between qubits in optical cavities. They employ an auxiliary qubit to report if a successful gate occurred. In this manner, the errors, which would have corrupted a deterministic gate, are converted into a nonunity probability of success: once successful, the gate has a much higher fidelity than a similar deterministic gate. Specifically, we describe that a heralded, near-deterministic controlled phase gate (CZ gate) with the conditional error arbitrarily close to zero and the success probability that approaches unity as the cooperativity of the system, C , becomes large. Furthermore, we describe an extension to near-deterministic N -qubit Toffoli gate with a favorable error scaling. These gates can be directly employed in quantum repeater networks to facilitate near-ideal entanglement swapping, thus greatly speeding up the entanglement distribution.

 

Title:
Martin Lewis Perl
Authors:
Feldman, Gary; Jaros, John; Schindler, Rafe H.
Publication:
Physics Today, vol. 68, issue 3, pp. 60-61
Publication Date:
03/2015
Origin:
CROSSREF
DOI:
10.1063/PT.3.2727
Bibliographic Code:
2015PhT....68c..60F

Abstract

Not Available

 

Title:
Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit
Authors:
Kolkowitz, S.; Safira, A.; High, A. A.; Devlin, R. C.; Choi, S.; Unterreithmeier, Q. P.; Patterson, D.; Zibrov, A. S.; Manucharyan, V. E.; Park, H.; Lukin, M. D.
Publication:
Science, Volume 347, Issue 6226, pp. 1129-1132 (2015). (Sci Homepage)
Publication Date:
03/2015
Category:
MAT SCI
Origin:
SCIENCE
Abstract Copyright:
(c) 2015: Science
DOI:
10.1126/science.aaa4298
Bibliographic Code:
2015Sci...347.1129K

Abstract

Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20 to 200 nanometers) and temperatures (10 to 300 kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, we find that Johnson noise is markedly suppressed next to single-crystal films, indicative of a substantial deviation from Ohm's law at length scales below the electron mean free path. Our results are consistent with a generalized model that accounts for the ballistic motion of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used for controlling nanoscale optoelectronic, atomic, and solid-state quantum systems.

 

Title:
Strongly correlated quantum walks in optical lattices
Authors:
Preiss, Philipp M.; Ma, Ruichao; Tai, M. Eric; Lukin, Alexander; Rispoli, Matthew; Zupancic, Philip; Lahini, Yoav; Islam, Rajibul; Greiner, Markus
Publication:
Science, Volume 347, Issue 6227, pp. 1229-1233 (2015). (Sci Homepage)
Publication Date:
03/2015
Category:
PHYSICS
Origin:
SCIENCE
Abstract Copyright:
(c) 2015: Science
DOI:
10.1126/science.1260364
Bibliographic Code:
2015Sci...347.1229P

Abstract

Full control over the dynamics of interacting, indistinguishable quantum particles is an important prerequisite for the experimental study of strongly correlated quantum matter and the implementation of high-fidelity quantum information processing. We demonstrate such control over the quantum walk---the quantum mechanical analog of the classical random walk---in the regime where dynamics are dominated by interparticle interactions. Using interacting bosonic atoms in an optical lattice, we directly observed fundamental effects such as the emergence of correlations in two-particle quantum walks, as well as strongly correlated Bloch oscillations in tilted optical lattices. Our approach can be scaled to larger systems, greatly extending the class of problems accessible via quantum walks.


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