Faculty Publications: June, 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:
Jan 2013 | Feb 2013 | Mar 2013 | Apr 2013 | May 2013 | June 2013 | July 2013 | Aug 2013 | Sep 2013 | Oct 2013 | Nov 2013 | Dec2013
Jan 2014 | Feb 2014 | Mar 2014 | Apr 2014 | May 2014 | June 2014 | July 2014 | Aug 2014 | Sep 2014 | Oct 2014 | Nov 2014 | Dec 2014
Jan 2015 | Feb 2015 | Mar 2015 | Apr 2015 | May 2015



Title:
Making sense of confusion: Relating performance, confidence, and self-efficacy to expressions of confusion in an introductory physics class
Authors:
Dowd, Jason E.; Araujo, Ives; Mazur, Eric
Publication:
Physical Review Special Topics - Physics Education Research, Volume 11, Issue 1, id.010107
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Research in physics education, Learning theory and science teaching
Abstract Copyright:
2015: authors
DOI:
10.1103/PhysRevSTPER.11.010107
Bibliographic Code:
2015PRSTP..11a0107D

Abstract

Although confusion is generally perceived to be negative, educators dating as far back as Socrates, who asked students to question assumptions and wrestle with ideas, have challenged this notion. Can confusion be productive? How should instructors interpret student expressions of confusion? During two semesters of introductory physics that involved Just-in-Time Teaching (JiTT) and research-based reading materials, we evaluated performance on reading assignments while simultaneously measuring students' self-assessment of their confusion over the preclass reading material (N =137 ; Nfall=106 , Nspring=88 ). We examined the relationship between confusion and correctness, confidence in reasoning, and (in the spring) precourse self-efficacy. We find that student expressions of confusion before coming to class are negatively related to correctness on preclass content-related questions, confidence in reasoning on those questions, and self-efficacy, but weakly positively related to final grade when controlling for these factors (beta =0.23 , p =0.03 ).

 

Title:
Response switching and self-efficacy in Peer Instruction classrooms
Authors:
Miller, Kelly; Schell, Julie; Ho, Andrew; Lukoff, Brian; Mazur, Eric
Publication:
Physical Review Special Topics - Physics Education Research, Volume 11, Issue 1, id.010104
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Education, General physics
Abstract Copyright:
2015: authors
DOI:
10.1103/PhysRevSTPER.11.010104
Bibliographic Code:
2015PRSTP..11a0104M

Abstract

Peer Instruction, a well-known student-centered teaching method, engages students during class through structured, frequent questioning and is often facilitated by classroom response systems. The central feature of any Peer Instruction class is a conceptual question designed to help resolve student misconceptions about subject matter. We provide students two opportunities to answer each question---once after a round of individual reflection and then again after a discussion round with a peer. The second round provides students the choice to "switch" their original response to a different answer. The percentage of right answers typically increases after peer discussion: most students who answer incorrectly in the individual round switch to the correct answer after the peer discussion. However, for any given question there are also students who switch their initially right answer to a wrong answer and students who switch their initially wrong answer to a different wrong answer. In this study, we analyze response switching over one semester of an introductory electricity and magnetism course taught using Peer Instruction at Harvard University. Two key features emerge from our analysis: First, response switching correlates with academic self-efficacy. Students with low self-efficacy switch their responses more than students with high self-efficacy. Second, switching also correlates with the difficulty of the question; students switch to incorrect responses more often when the question is difficult. These findings indicate that instructors may need to provide greater support for difficult questions, such as supplying cues during lectures, increasing times for discussions, or ensuring effective pairing (such as having a student with one right answer in the pair). Additionally, the connection between response switching and self-efficacy motivates interventions to increase student self-efficacy at the beginning of the semester by helping students develop early mastery or to reduce stressful experiences (i.e., high-stakes testing) early in the semester, in the hope that this will improve student learning in Peer Instruction classrooms.

 

Title:
Search for a Charged Higgs Boson Produced in the Vector-Boson Fusion Mode with Decay H±-->W±Z using p p Collisions at &surd;{s }=8 TeV with the ATLAS Experiment
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2819 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 23, id.231801 (PhRvL Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Extensions of electroweak Higgs sector
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevLett.114.231801
Bibliographic Code:
2015PhRvL.114w1801A

Abstract

A search for a charged Higgs boson, H±, decaying to a W± boson and a Z boson is presented. The search is based on 20.3 fb-1 of proton-proton collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. The H± boson is assumed to be produced via vector-boson fusion and the decays W±-->q q'¯ and Z -->e+e-/mu+mu- are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H± boson is observed. Upper limits of 31-1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H± boson times its branching fraction to W±Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.

 

Title:
Two-Dimensional Clusters of Colloidal Spheres: Ground States, Excited States, and Structural Rearrangements
Authors:
Perry, Rebecca W.; Holmes-Cerfon, Miranda C.; Brenner, Michael P.; Manoharan, Vinothan N.
Publication:
Physical Review Letters, Volume 114, Issue 22, id.228301 (PhRvL Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Colloids, Geometry differential geometry and topology, Stochastic analysis methods, Classical statistical mechanics
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.228301
Bibliographic Code:
2015PhRvL.114v8301P

Abstract

We study experimentally what is arguably the simplest yet nontrivial colloidal system: two-dimensional clusters of six spherical particles bound by depletion interactions. These clusters have multiple, degenerate ground states whose equilibrium distribution is determined by entropic factors, principally the symmetry. We observe the equilibrium rearrangements between ground states as well as all of the low-lying excited states. In contrast to the ground states, the excited states have soft modes and low symmetry, and their occupation probabilities depend on the size of the configuration space reached through internal degrees of freedom, as well as a single "sticky parameter" encapsulating the depth and curvature of the potential. Using a geometrical model that accounts for the entropy of the soft modes and the diffusion rates along them, we accurately reproduce the measured rearrangement rates. The success of this model, which requires no fitting parameters or measurements of the potential, shows that the free-energy landscape of colloidal systems and the dynamics it governs can be understood geometrically.

 

Title:
Wess-Zumino-Witten Terms in Graphene Landau Levels
Authors:
Lee, Junhyun; Sachdev, Subir
Publication:
Physical Review Letters, Volume 114, Issue 22, id.226801 (PhRvL Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Quantized spin models
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevLett.114.226801
Bibliographic Code:
2015PhRvL.114v6801L

Abstract

We consider the interplay between the antiferromagnetic and Kekulé valence bond solid orderings in the zero energy Landau levels of neutral monolayer and bilayer graphene. We establish the presence of Wess-Zumino-Witten terms between these orders: this implies that their quantum fluctuations are described by the deconfined critical theories of quantum spin systems. We present implications for experiments, including the possible presence of excitonic superfluidity in bilayer graphene.

 

Title:
Rotational State Microwave Mixing for Laser Cooling of Complex Diatomic Molecules
Authors:
Yeo, Mark; Hummon, Matthew T.; Collopy, Alejandra L.; Yan, Bo; Hemmerling, Boerge; Chae, Eunmi; Doyle, John M.; Ye, Jun
Publication:
Physical Review Letters, Volume 114, Issue 22, id.223003 (PhRvL Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Slowing and cooling of molecules, Trapping of molecules, Mechanical effects of light on atoms molecules and ions
Abstract Copyright:
(c) 2015: us
DOI:
10.1103/PhysRevLett.114.223003
Bibliographic Code:
2015PhRvL.114v3003Y

Abstract

We demonstrate the mixing of rotational states in the ground electronic state using microwave radiation to enhance optical cycling in the molecule yttrium (II) monoxide (YO). This mixing technique is used in conjunction with a frequency modulated and chirped continuous wave laser to slow longitudinally a cryogenic buffer-gas beam of YO. We generate a flux of YO below 10 m /s , directly loadable into a three-dimensional magneto-optical trap. This technique opens the door for laser cooling of diatomic molecules with more complex loss channels due to intermediate states.

 

Title:
Search for New Phenomena in Dijet Angular Distributions in Proton-Proton Collisions at &surd;{s }=8 TeV Measured with the ATLAS Detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2818 coauthors
Publication:
Physical Review Letters, Volume 114, Issue 22, id.221802 (PhRvL Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Composite models
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevLett.114.221802
Bibliographic Code:
2015PhRvL.114v1802A

Abstract

A search for new phenomena in LHC proton-proton collisions at a center-of-mass energy of &surd;{s }=8 TeV was performed with the ATLAS detector using an integrated luminosity of 17.3 fb-1 . The angular distributions are studied in events with at least two jets; the highest dijet mass observed is 5.5 TeV. All angular distributions are consistent with the predictions of the standard model. In a benchmark model of quark contact interactions, a compositeness scale below 8.1 TeV in a destructive interference scenario and 12.0 TeV in a constructive interference scenario is excluded at 95% C.L.; median expected limits are 8.9 TeV for the destructive interference scenario and 14.1 TeV for the constructive interference scenario.

 

Title:
Search for massive supersymmetric particles decaying to many jets using the ATLAS detector in p p collisions at &surd;{s }=8 TeV
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2829 coauthors
Publication:
Physical Review D, Volume 91, Issue 11, id.112016 (PhRvD Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Supersymmetric models, Supersymmetry, Experimental tests, Jets in large-Q2 scattering
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.112016
Bibliographic Code:
2015PhRvD..91k2016A

Abstract

Results of a search for decays of massive particles to fully hadronic final states are presented. This search uses 20.3 fb-1 of data collected by the ATLAS detector in &surd;{s }=8 TeV proton-proton collisions at the LHC. Signatures based on high jet multiplicities without requirements on the missing transverse momentum are used to search for R -parity-violating supersymmetric gluino pair production with subsequent decays to quarks. The analysis is performed using a requirement on the number of jets, in combination with separate requirements on the number of b -tagged jets, as well as a topological observable formed from the scalar sum of the mass values of large-radius jets in the event. Results are interpreted in the context of all possible branching ratios of direct gluino decays to various quark flavors. No significant deviation is observed from the expected Standard Model backgrounds estimated using jet counting as well as data-driven templates of the total-jet-mass spectra. Gluino pair decays to ten or more quarks via intermediate neutralinos are excluded for a gluino with mass mg ˜<1 TeV for a neutralino mass mchi˜10=500 GeV . Direct gluino decays to six quarks are excluded for mg ˜<917 GeV for light-flavor final states, and results for various flavor hypotheses are presented.

 

Title:
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton+jets final state with ATLAS
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2822 coauthors
Publication:
Physical Review D, Volume 91, Issue 11, id.112013 (PhRvD Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Top quarks
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.112013
Bibliographic Code:
2015PhRvD..91k2013A

Abstract

A measurement is presented of the t t ¯ inclusive production cross section in p p collisions at a center-of-mass energy of &surd;{s }=8 TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement was performed in the lepton+jets final state using a data set corresponding to an integrated luminosity of 20.3 fb-1 . The cross section was obtained using a likelihood discriminant fit and b -jet identification was used to improve the signal-to-background ratio. The inclusive t t ¯ production cross section was measured to be 260 ±1(stat)-23+22(stat)±8 (lumi)±4 (beam) pb assuming a top-quark mass of 172.5 GeV, in good agreement with the theoretical prediction of 253-15+13 pb . The t t ¯-->(e ,mu )+jets production cross section in the fiducial region determined by the detector acceptance is also reported.

 

Title:
Search for vectorlike B quarks in events with one isolated lepton, missing transverse momentum, and jets 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 2820 coauthors
Publication:
Physical Review D, Volume 91, Issue 11, id.112011 (PhRvD Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Limits on production of particles, Models beyond the standard model, Other particles
Abstract Copyright:
2015: CERN
DOI:
10.1103/PhysRevD.91.112011
Bibliographic Code:
2015PhRvD..91k2011A

Abstract

A search has been performed for pair production of heavy vectorlike down-type (B ) quarks. The analysis explores the lepton-plus-jets final state, characterized by events with one isolated charged lepton (electron or muon), significant missing transverse momentum, and multiple jets. One or more jets are required to be tagged as arising from b quarks, and at least one pair of jets must be tagged as arising from the hadronic decay of an electroweak boson. The analysis uses the full data sample of p p collisions recorded in 2012 by the ATLAS detector at the LHC, operating at a center-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb-1 . No significant excess of events is observed above the expected background. Limits are set on vectorlike B production, as a function of the B branching ratios, assuming the allowable decay modes are B -->W t /Z b /H b . In the chiral limit with a branching ratio of 100% for the decay B -->W t , the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 810 GeV (760 GeV). In the case where the vectorlike B quark has branching ratio values corresponding to those of an S U (2 ) singlet state, the observed (expected) 95% C.L. lower limit on the vectorlike B mass is 640 GeV (505 GeV). The same analysis, when used to investigate pair production of a colored, charge 5 /3 exotic fermion T5/3, with subsequent decay T5/3-->W t, sets an observed (expected) 95% C.L. lower limit on the T5/3 mass of 840 GeV (780 GeV).

 

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 107 coauthors (Minos Collaboration)
Publication:
Physical Review D, Volume 91, Issue 11, id.112006 (PhRvD Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Neutrino muon pion and other elementary particle detectors, cosmic ray detectors, Cosmic-ray interactions, Cosmic rays, Background radiations
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevD.91.112006
Bibliographic Code:
2015PhRvD..91k2006A

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:
Measurement of the production and differential cross sections of W+W- bosons in association with jets in p p ¯ collisions at &surd;{s }=1.96 TeV
Authors:
Aaltonen, T.; Amerio, S.; Amidei, D.;... Franklin, M.;... Guimaraes da Costa, J.;... and 398 coauthors
Publication:
Physical Review D, Volume 91, Issue 11, id.111101 (PhRvD Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
W bosons, Experimental tests, Applications of electroweak models to specific processes
Abstract Copyright:
2015: authors
DOI:
10.1103/PhysRevD.91.111101
Bibliographic Code:
2015PhRvD..91k1101A

Abstract

We present a measurement of the W-boson-pair production cross section in p p ¯ collisions at 1.96 TeV center-of-mass energy and the first measurement of the differential cross section as a function of jet multiplicity and leading-jet energy. The W+W- cross section is measured in the final state comprising two charged leptons and neutrinos, where either charged lepton can be an electron or a muon. Using data collected by the CDF experiment corresponding to 9.7 fb-1 of integrated luminosity, a total of 3027 collision events consistent with W+W- production are observed with an estimated background contribution of 1790 ±190 events. The measured total cross section is sigma (p p ¯ -->W+W-)=14.0 ±0.6 (stat)-1.0+1.2(syst)±0.8 (lumi) pb, consistent with the standard model prediction.

 

Title:
Imprint of topological degeneracy in quasi-one-dimensional fractional quantum Hall states
Authors:
Sagi, Eran; Oreg, Yuval; Stern, Ady; Halperin, Bertrand I.
Publication:
Physical Review B, Volume 91, Issue 24, id.245144 (PhRvB Homepage)
Publication Date:
06/2015
Origin:
APS
PACS Keywords:
Quantum Hall effects, Quantum wires, Phases: geometric, dynamic or topological, Multilayers superlattices heterostructures
Abstract Copyright:
2015: American Physical Society
DOI:
10.1103/PhysRevB.91.245144
Bibliographic Code:
2015PhRvB..91x5144S

Abstract

We consider an annular superconductor-insulator-superconductor Josephson junction, with the insulator being a double layer of electron and holes at Abelian fractional quantum Hall states of identical fillings. When the two superconductors gap out the edge modes, the system has a topological ground-state degeneracy in the thermodynamic limit akin to the fractional quantum Hall degeneracy on a torus. In the quasi-one-dimensional limit, where the width of the insulator becomes small, the ground-state energies are split. We discuss several implications of the topological degeneracy that survive the crossover to the quasi-one-dimensional limit. In particular, the Josephson effect shows a 2 pi d periodicity, where d is the ground-state degeneracy in the two-dimensional limit. We find that at special values of the relative phase between the two superconductors there are protected crossing points in which the degeneracy is not completely lifted. These features occur also if the insulator is a time-reversal-invariant fractional topological insulator. We describe the latter using a construction based on coupled wires. Furthermore, when the superconductors are replaced by systems with an appropriate magnetic order that gap the edges via a spin-flipping backscattering, the Josephson effect is replaced by a spin Josephson effect.

 

Title:
High-efficiency resonant amplification of weak magnetic fields for single spin magnetometry at room temperature
Authors:
Trifunovic, Luka; Pedrocchi, Fabio L.; Hoffman, Silas; Maletinsky, Patrick; Yacoby, Amir; Loss, Daniel
Publication:
Nature Nanotechnology, Volume 10, Issue 6, pp. 541-546 (2015).
Publication Date:
06/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nnano.2015.74
Bibliographic Code:
2015NatNa..10..541T

Abstract

Magnetic resonance techniques not only provide powerful imaging tools that have revolutionized medicine, but they have a wide spectrum of applications in other fields of science such as biology, chemistry, neuroscience and physics. However, current state-of-the-art magnetometers are unable to detect a single nuclear spin unless the tip-to-sample separation is made sufficiently small. Here, we demonstrate theoretically that by placing a ferromagnetic particle between a nitrogen--vacancy magnetometer and a target spin, the magnetometer sensitivity is improved dramatically. Using materials and techniques that are already experimentally available, our proposed set-up is sensitive enough to detect a single nuclear spin within ten milliseconds of data acquisition at room temperature. The sensitivity is practically unchanged when the ferromagnet surface to the target spin separation is smaller than the ferromagnet lateral dimensions; typically about a tenth of a micrometre. This scheme further benefits when used for nitrogen--vacancy ensemble measurements, enhancing sensitivity by an additional three orders of magnitude.

 

Title:
Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platform
Authors:
Cui, Xu; Lee, Gwan-Hyoung; Kim, Young Duck; Arefe, Ghidewon; Huang, Pinshane Y.; Lee, Chul-Ho; Chenet, Daniel A.; Zhang, Xian; Wang, Lei; Ye, Fan; Pizzocchero, Filippo; Jessen, Bjarke S.; Watanabe, Kenji; Taniguchi, Takashi; Muller, David A.; Low, Tony; Kim, Philip; Hone, James
Publication:
Nature Nanotechnology, Volume 10, Issue 6, pp. 534-540 (2015).
Publication Date:
06/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nnano.2015.70
Bibliographic Code:
2015NatNa..10..534C

Abstract

Atomically thin two-dimensional semiconductors such as MoS2 hold great promise for electrical, optical and mechanical devices and display novel physical phenomena. However, the electron mobility of mono- and few-layer MoS2 has so far been substantially below theoretically predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviours. Potential sources of disorder and scattering include defects such as sulphur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielectrics. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and electrically contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements in performance, including a record-high Hall mobility reaching 34,000 cm2 V--1 s--1 for six-layer MoS2 at low temperature, confirming that low-temperature performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also observed Shubnikov--de Haas oscillations in high-mobility monolayer and few-layer MoS2. Modelling of potential scattering sources and quantum lifetime analysis indicate that a combination of short-range and long-range interfacial scattering limits the low-temperature mobility of MoS2.

 

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:
Nature Materials, Volume 14, Issue 6, pp. 583-588 (2015).
Publication Date:
06/2015
Origin:
NATURE
Abstract Copyright:
(c) 2015: Nature Publishing Group
DOI:
10.1038/nmat4222
Bibliographic Code:
2015NatMa..14..583W

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's 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:
Evaluation of intergranular exchange coupling and magnetic domain size in CoCrPt--SiOX thin films with perpendicular anisotropy
Authors:
Papusoi, C.; Desai, M.; Acharya, R.
Publication:
Journal of Physics D: Applied Physics, Volume 48, Issue 21, article id. 215005 (2015).
Publication Date:
06/2015
Origin:
IOP
DOI:
10.1088/0022-3727/48/21/215005
Bibliographic Code:
2015JPhD...48u5005P

Abstract

A method to evaluate the intergranular exchange coupling constant JEX in thin films with perpendicular anisotropy, based on first order reversal curve (FORC) diagrams, is proposed. For a 7.5 nm thick CoCrPt--SiOx magnetic (MAG) layer, JEX can be decreased from 1.1 to 0.26 erg cm-2 by using an adjacent CoCr--TiOx layer (isolation enhancement layer or IEL), enabling its application for high-density magnetic recording. The minimum value of JEX is attained for an IEL thickness of ~1.5 nm, which is low enough to preserve the HCP crystallographic structure of the MAG layer, with the c-axis perpendicular to film plane. The extracted values of JEX are used to evaluate the magnetic domain size of MAG layer using the checkerboard and the stripe domain models. Magnetic force microscopy observations indicate that domain size approaches the value predicted by the checkerboard model when JEX ≈ 0.8 erg cm-2, while for JEX > 0.8 erg cm-2 the actual domain size lies between the values indicated by the two models.

 

Title:
Scaling dimensions of monopole operators in the theory in 2 + 1 dimensions
Authors:
Dyer, Ethan; Mezei, Márk; Pufu, Silviu S.; Sachdev, Subir
Publication:
Journal of High Energy Physics, Volume 2015, article id. #37, 48 pp.
Publication Date:
06/2015
Origin:
SPRINGER
Keywords:
Solitons Monopoles and Instantons, 1/N Expansion
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP06(2015)037
Bibliographic Code:
2015JHEP...06..037D

Abstract

We study monopole operators at the conformal critical point of the theory in 2+1 spacetime dimensions. Using the state-operator correspondence and a saddle point approximation, we compute the scaling dimensions of the operators that insert one or two units of magnetic flux to next-to-leading order in 1 /N b . We compare our results to numerical studies of quantum antiferromagnets on two-dimensional lattices with SU( N b ) global symmetry, using the mapping of the monopole operators to valence bond solid order parameters of the lattice antiferromagnet. For the monopole operators that insert three or more units of magnetic flux, we find that the rotationally-symmetric saddle point is unstable; in order to obtain the scaling dimensions of these operators, even at leading order in 1 /N b , one should consider non-spherically-symmetric saddles.

 

Title:
Erratum to: On the classification of 6D SCFTs and generalized ADE orbifolds
Authors:
Heckman, Jonathan J.; Morrison, David R.; Vafa, Cumrun
Publication:
Journal of High Energy Physics, Volume 2015, article id. #17, 2 pp.
Publication Date:
06/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: The Author(s)
DOI:
10.1007/JHEP06(2015)017
Bibliographic Code:
2015JHEP...06..017H

Abstract

Not Available

 

Title:
Rotational spectroscopy and three-wave mixing of 4-carvomenthenol: A technical guide to measuring chirality in the microwave regime
Authors:
Shubert, V. Alvin; Schmitz, David; Medcraft, Chris; Krin, Anna; Patterson, David; Doyle, John M.; Schnell, Melanie
Publication:
The Journal of Chemical Physics, Volume 142, Issue 21, id.214201 (JChPh Homepage)
Publication Date:
06/2015
Origin:
AIP
Abstract Copyright:
2015: AIP Publishing LLC
DOI:
10.1063/1.4921833
Bibliographic Code:
2015JChPh.142u4201S

Abstract

We apply chirality sensitive microwave three-wave mixing to 4-carvomenthenol, a molecule previously uncharacterized with rotational spectroscopy. We measure its rotational spectrum in the 2-8.5 GHz range and observe three molecular conformers. We describe our method in detail, from the initial step of spectral acquisition and assignment to the final step of determining absolute configuration and enantiomeric excess. Combining fitted rotational constants with dipole moment components derived from quantum chemical calculations, we identify candidate three-wave mixing cycles which were further tested using a double resonance method. Initial optimization of the three-wave mixing signal is done by varying the duration of the second excitation pulse. With known transition dipole matrix elements, absolute configuration can be directly determined from a single measurement.

 

Title:
Search for a new resonance decaying to a W or Z boson and a Higgs boson in the final states with the ATLAS detector
Authors:
Aad, G.; Abbott, B.; Abdallah, J.;... Barreiro Guimarães da Costa, J.;... Franklin, M.;... Huth, J.;... Morii, M.;... and 2818 coauthors
Publication:
The European Physical Journal C, Volume 75, article id. #263, 21 pp. (EPJC Homepage)
Publication Date:
06/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: CERN for the benefit of the ATLAS collaboration
DOI:
10.1140/epjc/s10052-015-3474-x
Bibliographic Code:
2015EPJC...75..263A

Abstract

A search for a new resonance decaying to a W or Z boson and a Higgs boson in the final states is performed using 20.3 fb of pp collision data recorded at 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.

 

Title:
Extremal Bundles on Calabi-Yau Threefolds
Authors:
Gao, Peng; He, Yang-Hui; Yau, Shing-Tung
Publication:
Communications in Mathematical Physics, Volume 336, Issue 3, pp.1167-1200
Publication Date:
06/2015
Origin:
SPRINGER
Abstract Copyright:
(c) 2015: Springer-Verlag Berlin Heidelberg
DOI:
10.1007/s00220-014-2271-y
Bibliographic Code:
2015CMaPh.336.1167G

Abstract

We study constructions of stable holomorphic vector bundles on Calabi-Yau threefolds, especially those with exact anomaly cancellation which we call extremal. By going through the known databases we find that such examples are rare in general and can be ruled out for the spectral cover construction for all elliptic threefolds. We then introduce a general Hartshorne-Serre construction and use it to find extremal bundles of general ranks and study their stability, as well as computing their Chern numbers. Based on both existing and our new constructions, we revisit the DRY conjecture for the existence of stable sheaves on Calabi-threefolds, and provide theoretical and numerical evidence for its correctness. Our construction can be easily generalized to bundles with no extremal conditions imposed.

 

Title:
Absence of disorder-driven metal-insulator transitions in simple holographic models
Authors:
Grozdanov, Saso; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad
Publication:
eprint arXiv:1507.00003
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons
Comment:
6 pages. v2: more references, minor changes
Bibliographic Code:
2015arXiv150700003G

Abstract

We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to Einstein-Maxwell theory in an asymptotically $\mathrm{AdS}_4$ spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond non-perturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

 

Title:
\textit{Ab-initio} Tight-Binding Hamiltonian for Transition Metal Dichalcogenides
Authors:
Fang, Shiang; Kuate Defo, Rodrick; Shirodkar, Sharmila; Lieu, Simon; Tritsaris, Georgios; Kaxiras, Efthimios
Publication:
eprint arXiv:1506.08860
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
16 pages, 9 figures
Bibliographic Code:
2015arXiv150608860F

Abstract

We present an accurate \textit{ab-initio} tight-binding hamiltonian for the transition-metal dichalcogenides, MoS$_2$, MoSe$_2$, WS$_2$, WSe$_2$, with a minimal basis (the \textit{d} orbitals for the metal atoms and \textit{p} orbitals for the chalcogen atoms) based on a transformation of the Kohn-Sham density function theory (DFT) hamiltonian to a basis of maximally localized Wannier functions (MLWF). The truncated tight-binding hamiltonian (TBH), with only on-site, first and partial second neighbor interactions, including spin-orbit coupling, provides a simple physical picture and the symmetry of the main band-structure features. Interlayer interactions between adjacent layers are modeled by transferable hopping terms between the chalcogen \textit{p} orbitals. The full-range tight-binding hamiltonian (FTBH) can be reduced to hybrid-orbital k $\cdot$ p effective hamiltonians near the band extrema that captures important low-energy excitations. These \textit{ab-initio} hamiltonians can serve as the starting point for applications to interacting many-body physics including optical transitions and Berry curvature of bands, of which we give some examples.

 

Title:
A structural approach to relaxation in glassy liquids
Authors:
Schoenholz, Samuel S.; Cubuk, Ekin D.; Kaxiras, Efthimios; Liu, Andrea J
Publication:
eprint arXiv:1506.07772
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Soft Condensed Matter
Bibliographic Code:
2015arXiv150607772S

Abstract

When a liquid freezes, a change in the local atomic structure marks the transition to the crystal. When a liquid is cooled to form a glass, however, no noticeable structural change marks the glass transition. Indeed, characteristic features of glassy dynamics that appear below an onset temperature, T_0, are qualitatively captured by mean field theory, which assumes uniform local structure at all temperatures. Even studies of more realistic systems have found only weak correlations between structure and dynamics. This begs the question: is structure important to glassy dynamics in three dimensions? Here, we answer this question affirmatively by using machine learning methods to identify a new field, that we call softness, which characterizes local structure and is strongly correlated with rearrangement dynamics. We find that the onset of glassy dynamics at T_0 is marked by the onset of correlations between softness (i.e. structure) and dynamics. Moreover, we use softness to construct a simple model of slow glassy relaxation that is in excellent agreement with our simulation results, showing that a theory of the evolution of softness in time would constitute a theory of glassy dynamics.

 

Title:
Visualization of phase-coherent electron interference in a ballistic graphene Josephson junction
Authors:
Allen, M. T.; Shtanko, O.; Fulga, I. C.; Wang, J. I.-J.; Nurgaliev, D.; Watanabe, K.; Taniguchi, T.; Akhmerov, A. R.; Jarillo-Herrero, P.; Levitov, L. S.; Yacoby, A.
Publication:
eprint arXiv:1506.06734
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity
Comment:
Includes Supplementary Information
Bibliographic Code:
2015arXiv150606734A

Abstract

Interference of standing waves in electromagnetic resonators forms the basis of many technologies, from telecommunications and spectroscopy to detection of gravitational waves. However, unlike the confinement of light waves in vacuum, the interference of electronic waves in solids is complicated by boundary properties of the crystal, notably leading to electron guiding by atomic-scale potentials at the edges. Understanding the microscopic role of boundaries on coherent wave interference is an unresolved question due to the challenge of detecting charge flow with submicron resolution. Here we employ Fraunhofer interferometry to achieve real-space imaging of cavity modes in a graphene Fabry-Perot resonator, embedded between two superconductors to form a Josephson junction. By directly visualizing current flow using Fourier methods, our measurements reveal surprising redistribution of current on and off resonance. These findings provide direct evidence of separate interference conditions for edge and bulk currents and reveal the ballistic nature of guided edge states. Beyond equilibrium, our measurements show strong modulation of the multiple Andreev reflection amplitude on an off resonance, a direct measure of the gate-tunable change of cavity transparency. These results demonstrate that, contrary to the common belief, electron interactions with realistic disordered edges facilitate electron wave interference and ballistic transport.

 

Title:
Fast, label-free tracking of single viruses and weakly scattering nanoparticles in a nano-fluidic optical fiber
Authors:
Faez, Sanli; Lahini, Yoav; Weidlich, Stefan; Garmann, Rees F.; Wondraczek, Katrin; Zeisberger, Matthias; Schmidt, Markus A.; Orrit, Michel; Manoharan, Vinothan N.
Publication:
eprint arXiv:1506.06500
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Physics - Optics, Condensed Matter - Soft Condensed Matter
Comment:
11 pages, 4 figures, supplementary information
Bibliographic Code:
2015arXiv150606500F

Abstract

High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber containing a sub-wavelength, nano-fluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylinderical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions - 4.6 megadaltons in size - at rates of over 2 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.

 

Title:
Real space Eliashberg approach to charge order of electrons coupled to dynamic antiferromagnetic fluctuations
Authors:
Bauer, Johannes; Sachdev, Subir
Publication:
eprint arXiv:1506.06136
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Superconductivity
Comment:
9 pages, 8 figures
Bibliographic Code:
2015arXiv150606136B

Abstract

We study charge ordered solutions for fermions on a square lattice interacting with dynamic antiferromagnetic fluctuations. Our approach is based on real space Eliashberg equations which are solved self-consistently. We first show that the antiferromagnetic fluctuations can induce arc features in the spectral functions, as spectral weight is suppressed at the hot spots; however, no real pseudogap is generated. At low temperature spontaneous charge order with a $d$-form factor can be stabilized for certain parameters. As long as the interacting Fermi surfaces possesses hot spots, the ordering wave vector corresponds to the diagonal connection of the hot spots, similar to the non-self-consistent case. Tendencies towards observed axial order only appear in situations without hot spots.

 

Title:
Bekenstein-Hawking Entropy and Strange Metals
Authors:
Sachdev, Subir
Publication:
eprint arXiv:1506.05111
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Condensed Matter - Strongly Correlated Electrons, General Relativity and Quantum Cosmology
Comment:
23 pages, 2 figures; (v2 and v3) added refs
Bibliographic Code:
2015arXiv150605111S

Abstract

We examine models of fermions with infinite-range interactions which realize non-Fermi liquids with a continuously variable U(1) charge density $\mathcal{Q}$, and a non-zero entropy density $\mathcal{S}$ at vanishing temperature. Real time correlators of operators carrying U(1) charge $q$ at a low temperature $T$ are characterized by a $\mathcal{Q}$-dependent frequency $\omega_{\mathcal{S}} = (q \, T/\hbar) (\partial \mathcal{S}/\partial{\mathcal{Q}})$ which determines a spectral asymmetry. We show that the correlators match precisely with those of the AdS$_2$ horizons of extremal charged black holes. On the black hole side, the matching requires $\mathcal{S}$ to be equal to the Bekenstein-Hawking entropy density, and employs the laws of black hole thermodynamics which relate $(\partial{\mathcal{S}}/\partial{\mathcal{Q}})/(2 \pi)$ to the electric field strength in AdS$_2$. The fermion model entropy is computed using the microscopic degrees of freedom of a UV complete theory without supersymmetry.

 

Title:
Probing excitations in insulators via injection of spin currents
Authors:
Chatterjee, Shubhayu; Sachdev, Subir
Publication:
eprint arXiv:1506.04740
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
21+4 pages, 4 figures
Bibliographic Code:
2015arXiv150604740C

Abstract

We propose a spin transport experiment to measure the low-energy excitations in insulators with spin degrees of freedom, with a focus on detecting ground states that lack magnetic order. A general formalism to compute the spin current from a metal with a non-equilibrium distribution of spins to an insulator is developed. It is applied to insulating states with and without long range magnetic order, and salient features in the spin conductance are noted.

 

Title:
Weak Gravity Strongly Constrains Large-Field Axion Inflation
Authors:
Heidenreich, Ben; Reece, Matthew; Rudelius, Tom
Publication:
eprint arXiv:1506.03447
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
33 pages, 1 figure
Bibliographic Code:
2015arXiv150603447H

Abstract

Models of large-field inflation based on axion-like fields with shift symmetries can be simple and natural, and make a promising prediction of detectable primordial gravitational waves. The Weak Gravity Conjecture is known to constrain the simplest case in which a single axion descends from a gauge field in an extra dimension. By supplementing the Weak Gravity Conjecture with considerations of how the mass spectrum of the theory varies across the axion moduli space, we obtain more powerful constraints that apply to a variety of multi-axion theories including N-flation and alignment models. In every case that we consider, plausible assumptions lead to field ranges that cannot be parametrically larger than the Planck scale. Our results are strongly suggestive of a general inconsistency in models of large-field inflation based on axions, and possibly of a more general principle forbidding super-Planckian field ranges.

 

Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Publication:
eprint arXiv:1506.03077
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Materials Science, Condensed Matter - Soft Condensed Matter, Condensed Matter - Strongly Correlated Electrons
Comment:
10 pages, 5 figures
Bibliographic Code:
2015arXiv150603077M

Abstract

We extend the Weak Crystallization theory to the case of metallic alloys. The additional ingredient -- itinerant electrons -- generates nontrivial dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of FCC, Rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. The condition for stability of iQC that we find, is consistent with the Hume-Rothery rules known empirically for majority of stable iQC; namely, the length of the primary Bragg peak wavevector is approximately equal to the diameter of the Fermi surface.

 

Title:
New Symmetries of QED
Authors:
Kapec, Daniel; Pate, Monica; Strominger, Andrew
Publication:
eprint arXiv:1506.02906
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, High Energy Physics - Phenomenology
Comment:
17 pages
Bibliographic Code:
2015arXiv150602906K

Abstract

The soft photon theorem in U(1) gauge theories with only massless charged particles has recently been shown to be the Ward identity of an infinite-dimensional asymptotic symmetry group. This symmetry group is comprised of gauge transformations which approach angle-dependent constants at null infinity. In this paper, we extend the analysis to all U(1) theories, including those with massive charged particles such as QED.

 

Title:
Airy Equation for the Topological String Partition Function in a Scaling Limit
Authors:
Alim, Murad; Yau, Shing-Tung; Zhou, Jie
Publication:
eprint arXiv:1506.01375
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
High Energy Physics - Theory, Mathematical Physics, Mathematics - Algebraic Geometry
Comment:
11 pages, 1 figure
Bibliographic Code:
2015arXiv150601375A

Abstract

We use the polynomial formulation of the holomorphic anomaly equations governing perturbative topological string theory to derive the free energies in a scaling limit to all orders in perturbation theory for any Calabi-Yau threefold. The partition function in this limit satisfies an Airy differential equation in a rescaled topological string coupling. One of the two solutions of this equation gives the perturbative expansion and the other solution provides geometric hints of the non-perturbative structure of topological string theory. Both solutions can be expanded naturally around strong coupling.

 

Title:
Spin Superfluidity in the $\nu=0$ Quantum Hall State of Graphene
Authors:
Takei, So; Yacoby, Amir; Halperin, Bertrand I.; Tserkovnyak, Yaroslav
Publication:
eprint arXiv:1506.01061
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Mesoscale and Nanoscale Physics
Comment:
5 pages; 5 figures
Bibliographic Code:
2015arXiv150601061T

Abstract

A proposal to detect the purported canted antiferromagnet order for the $\nu=0$ quantum Hall state of graphene based on a two-terminal spin transport setup is theoretically discussed. In the presence of a magnetic field normal to the graphene plane, a dynamic and inhomogeneous texture of the N\'eel vector lying within the plane should mediate (nearly dissipationless) superfluid transport of spin angular momentum polarized along the $z$ axis, which could serve as a strong support for the canted antiferromagnet scenario. Spin injection and detection can be achieved by coupling two spin-polarized edge channels of the $|\nu|=2$ quantum Hall state on two opposite ends of the $\nu=0$ region. A simple kinetic theory and Onsager reciprocity are invoked to model the spin injection and detection processes, and the transport of spin through the antiferromagnet is accounted for using the Landau-Lifshitz-Gilbert phenomenology.

 

Title:
$1/f^\alpha$ noise and generalized diffusion in random Heisenberg spin systems
Authors:
Agarwal, Kartiek; Demler, Eugene; Martin, Ivar
Publication:
eprint arXiv:1506.00643
Publication Date:
06/2015
Origin:
ARXIV
Keywords:
Condensed Matter - Disordered Systems and Neural Networks
Comment:
22 pages, 21 figures
Bibliographic Code:
2015arXiv150600643A

Abstract

We study the 'flux noise' spectrum of random-bond quantum Heisenberg spin systems using a real-space renormalization group (RSRG) procedure that accounts for both the renormalization of the system Hamiltonian and of a generic probe that measures the noise. For spin chains, we find that the dynamical structure factor $S_q(f)$, at finite wave-vector $q$, exhibits a power-law behavior both at high and low frequencies $f$, with exponents that are connected to one another and to an anomalous dynamical exponent through relations that differ at $T = 0$ and $T = \infty$. The low-frequency power-law behavior of the structure factor is inherited by any generic probe with a finite band-width and is of the form $1/f^\alpha$ with $0.5 < \alpha < 1$. An analytical calculation of the structure factor, assuming a limiting distribution of the RG flow parameters (spin size, length, bond strength) confirms numerical findings. More generally, we demonstrate that this form of the structure factor, at high temperatures, is a manifestation of anomalous diffusion which directly follows from a generalized spin-diffusion propagator. We also argue that $1/f$-noise is intimately connected to many-body-localization at finite temperatures. In two dimensions, the RG procedure is less reliable; however, it becomes convergent for quasi-one-dimensional geometries where we find that one-dimensional $1/f^\alpha$ behavior is recovered at low frequencies; the latter configurations are likely representative of paramagnetic spin networks that produce $1/f^\alpha$ noise in SQUIDs.

 

Title:
Electric field effects in graphene/LaAlO3/SrTiO3 heterostructures and nanostructures
Authors:
Huang, Mengchen; Jnawali, Giriraj; Hsu, Jen-Feng; Dhingra, Shonali; Lee, Hyungwoo; Ryu, Sangwoo; Bi, Feng; Ghahari, Fereshte; Ravichandran, Jayakanth; Chen, Lu; Kim, Philip; Eom, Chang-Beom; D'Urso, Brian; Irvin, Patrick; Levy, Jeremy
Publication:
APL Materials, Volume 3, Issue 6, id.062502
Publication Date:
06/2015
Origin:
AIP
Abstract Copyright:
2015: Author(s)
DOI:
10.1063/1.4916098
Bibliographic Code:
2015APLM....3f2502H

Abstract

We report the development and characterization of graphene/LaAlO3/SrTiO3 heterostructures. Complex-oxide heterostructures are created by pulsed laser deposition and are integrated with graphene using both mechanical exfoliation and transfer from chemical-vapor deposition on ultraflat copper substrates. Nanoscale control of the metal-insulator transition at the LaAlO3/SrTiO3 interface, achieved using conductive atomic force microscope lithography, is demonstrated to be possible through the graphene layer. LaAlO3/SrTiO3-based electric field effects using a graphene top gate are also demonstrated. The ability to create functional field-effect devices provides the potential of graphene-complex-oxide heterostructures for scientific and technological advancement.

 

Title:
BICEP2/Keck Array. IV. Optical Characterization and Performance of the BICEP2 and Keck Array Experiments
Authors:
BICEP2 and Keck Array Collaborations; Ade, P. A. R.; Aikin, R. W.; Barkats, D.; Benton, S. J.; Bischoff, C. A.; Bock, J. J.; Bradford, K. J.; Brevik, J. A.; Buder, I.; Bullock, E.; Dowell, C. D.; Duband, L.; Filippini, J. P.; Fliescher, S.; Golwala, S. R.; Halpern, M.; Hasselfield, M.; Hildebrandt, S. R.; Hilton, G. C.; Hui, H.; Irwin, K. D.; Kang, J. H.; Karkare, K. S.; Kaufman, J. P.; Keating, B. G.; Kefeli, S.; Kernasovskiy, S. A.; Kovac, J. M.; Kuo, C. L.; Leitch, E. M.; Lueker, M.; Megerian, K. G.; Netterfield, C. B.; Nguyen, H. T.; O'Brient, R.; Ogburn, R. W., IV; Orlando, A.; Pryke, C.; Richter, S.; Schwarz, R.; Sheehy, C. D.; Staniszewski, Z. K.; Sudiwala, R. V.; Teply, G. P.; Thompson, K.; Tolan, J. E.; Turner, A. D.; Vieregg, A. G.; Weber, A. C.; Wong, C. L.; Yoon, K. W.
Publication:
The Astrophysical Journal, Volume 806, Issue 2, article id. 206, 23 pp. (2015). (ApJ Homepage)
Publication Date:
06/2015
Origin:
IOP
Astronomy Keywords:
cosmic background radiation, cosmology: observations, gravitational waves, inflation, polarization
DOI:
10.1088/0004-637X/806/2/206
Bibliographic Code:
2015ApJ...806..206A

Abstract

bicep2 and the Keck Array are polarization-sensitive microwave telescopes that observe the cosmic microwave background (CMB) from the South Pole at degree angular scales in search of a signature of inflation imprinted as B-mode polarization in the CMB. bicep2 was deployed in late 2009, observed for three years until the end of 2012 at 150 GHz with 512 antenna-coupled transition edge sensor bolometers, and has reported a detection of B-mode polarization on degree angular scales. The Keck Array was first deployed in late 2010 and will observe through 2016 with five receivers at several frequencies (95, 150, and 220 GHz). bicep2 and the Keck Array share a common optical design and employ the field-proven bicep1 strategy of using small-aperture, cold, on-axis refractive optics, providing excellent control of systematics while maintaining a large field of view. This design allows for full characterization of far-field optical performance using microwave sources on the ground. Here we describe the optical design of both instruments and report a full characterization of the optical performance and beams of bicep2 and the Keck Array at 150 GHz.


 go to Raw Search Results for the last 30 days

The raw results file is generated automatically and provides up-to-date listings of all faculty publications added to the database during the 30 last days. However, it is likely to include irrelevant results: i.e., authors who are not affiliated with Harvard Physics Department, but whose names happen to be identical to those of our faculty members, as well as all publications which were added to the database in the last 30 days, but may have been published months or even years ago.

 go to the Top


Smithsonian/NASA ADS Homepage | Query Form | Basic Search | HELP | FAQ