Quantum Matter

Displaying 385 - 396 of 439

Effect of thermal fluctuations in topological p-wave superconductors

Bela Bauer Microsoft Corporation
September 21, 2012

PIRSA:12090039
Condensed Matter
Hamiltonian Theory of Fractional Chern Bands

Ramamurti Shankar Yale University
September 14, 2012

PIRSA:12090047
Mathematical physics
Charge fractionalization and entanglement entropy for compressible phases in holography

Liza Huijse Karius, Inc.
September 11, 2012

PIRSA:12090059
Condensed Matter
Multiplets in the Entanglement Spectrum

Ari Turner Universiteit van Amsterdam

September 06, 2012

PIRSA:12090056
Topological Order in Spin Systems

Paul Fendley University of Oxford
August 10, 2012

PIRSA:12080002
Particle Physics
Glass: The Cinderella Problem of Condensed Matter Physics

Anthony Leggett University of Illinois Urbana-Champaign
August 03, 2012

PIRSA:12080001
Condensed Matter
Integer Quantum Hall Effect for Bosons: A Physical Realization

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
July 27, 2012

PIRSA:12070013
Condensed Matter
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects

Ashvin Vishwanath Harvard University
July 27, 2012

PIRSA:12070012
Condensed Matter
Entanglement, Holography, and the Quantum Phases of Matter

Subir Sachdev Harvard University

July 13, 2012

PIRSA:12070010
Entangling Superconductivity and antiferromagnetism: Quantum Monte Carlo without the sign Problem

Subir Sachdev Harvard University
July 11, 2012

PIRSA:12070009
Condensed Matter
Pyrochlore Material Yb_2Ti_2O_7: A Model Quantum Spin Ice
June 15, 2012

PIRSA:12060072
Condensed Matter
Relaxation in Driven Integer Quantum Hall Edge States

John Chalker University of Oxford
June 01, 2012

PIRSA:12060000
Mathematical physics

Effect of thermal fluctuations in topological p-wave superconductors

Bela Bauer Microsoft Corporation
September 21, 2012

PIRSA:12090039
Condensed Matter
In this talk, I will present our recent work on the effect of thermal fluctuations on the topological stability of chiral p-wave superconductors. We consider two models of superconductors: spinless and spinful with a focus on topological properties and Majorana zero-energy modes. We show that proliferation of vortex-antivortex pairs above the Kosterlitz-Thouless temperature T_KT drives the transition from a thermal Quantum Hall insulator to a thermal metal/insulator, and dramatically modifies the ground-state degeneracy splitting. This shows that in order to utilize 2D chiral p-wave superconductors for topological quantum computing, the temperature should be much smaller than T_KT. Within the spinful chiral p-wave model, we also investigate the interplay between half-quantum vortices carrying Majorana zero-energy modes and full-quantum vortices having trivial topological charge, and discuss topological properties of half-quantum vortices in the background of proliferating full-quantum vortices.
Hamiltonian Theory of Fractional Chern Bands

Ramamurti Shankar Yale University
September 14, 2012

PIRSA:12090047
Mathematical physics
It has been known for some time that a system with a filled band will have an integer quantum Hall conductance equal to its Chern number, a toplogical index associated with the band. While this is true for a system in a magnetic field with filled Landau Levels, even a system in zero external field can exhibit the QHE if its band has a Chern number. I review this issue and discuss a more recent question of whether a partially filled Chern band can exhibit the Fractional QHE. I describe the work done with Ganpathy Murthy in which we show how composite fermions, which were so useful in explaining the usual FQHE, can be introduced here and with equal success by adapting our Hamiltonian Theory of CFs developed for the FQHE in the continuum.
Charge fractionalization and entanglement entropy for compressible phases in holography

Liza Huijse Karius, Inc.
September 11, 2012

PIRSA:12090059
Condensed Matter
Multiplets in the Entanglement Spectrum

Ari Turner Universiteit van Amsterdam

September 06, 2012

PIRSA:12090056

What information can be determined about a state given just the ground state wave function? Quantum ground states, speaking intuitively, contain fluctuations between many of the configurations one might want to understand. The information about them can be organized by introducing an imaginary system, dubbed the entanglement Hamiltonian. What light does the dynamics of this Hamiltonian (a precise version of the notion of "zero point motion") shed on the actual system?

I will start my discussion near critical points, where Lorentz invariance often emerges and the entanglement Hamiltonian becomes tractable, revealing that it exists in one dimension less than the real system. One application is to the fluctuations of angular momentum in a spin chain.

The entanglement Hamiltonian is especially successful at clarifying the properties of quantum phases without order, such as topological insulators. In particular, spin chains often have no long range order due to quantum fluctuations. Nevertheless there can be phase transitions between two of these disordered states, suggesting the existence of a hidden order.

My main aim in the talk will be to demonstrate that the entanglement spectrum can serve as an order parameter for these unusual transitions; this observation leads to a classification of one-dimensional phases. One can understand the phases of the actual system simply by looking at the spectrum of the entanglement Hamiltonian, just as one deduces the properties of atoms from their spectra.
Topological Order in Spin Systems

Paul Fendley University of Oxford
August 10, 2012

PIRSA:12080002
Particle Physics
Much effort has been devoted to the study of systems with topological order, motivated by practical issues as well as more field theoretical and mathematical concerns. This talk will give an overview of some of the field, describing abelian systems relevant to the search for spin liquids, and non-abelian systems relevant to topological quantum computation. I will focus in particular on problems not reducible to free-fermion ones; examples include the RVB state of electrons as well as models of quantum loops and nets.
Glass: The Cinderella Problem of Condensed Matter Physics

Anthony Leggett University of Illinois Urbana-Champaign
August 03, 2012

PIRSA:12080001
Condensed Matter
Amorphous materials (glasses) probably constitute >90% of the solid matter surrounding us in everyday life,yet traditional textbooks of condensed matter physics devote virtually no space to them.Crudely speaking,the puzzles in the behavior of glasses can be divided into three major areas:the glass transition itself,the characteristic long-term memory effects and the near-equilibrium thermal,dielectric and transport properties;this talk focusses entirely on the third area.Over the last 40 years it has become apparent that the thermal and transport properties are not only qualitatively universal between glasses with totally different chemistry and microstructure,but in some cases possess a truly mind-boggling degree of _quantitative_ universality.In this talk I will describe the salient experimental data,review the established ("tunnelling two-level system") model commonly used to interpret them,and introduce a rather different scenario (developed in collaboration with D.C.Vural) which holds out some prospect of explaining the universalities in a natural way.
Integer Quantum Hall Effect for Bosons: A Physical Realization

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
July 27, 2012

PIRSA:12070013
Condensed Matter
A simple physical realization of an integer quantum Hall state of interacting two dimensional bosons is provided. This is an example of a "symmetry-protected topological" (SPT) phase which is a generalization of the concept of topological insulators to systems of interacting bosons or fermions. Universal physical properties of the boson integer quantum Hall state are described and shown to correspond to those expected from general classifications of SPT phases.
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects

Ashvin Vishwanath Harvard University
July 27, 2012

PIRSA:12070012
Condensed Matter
I will briefly review topological phases of non interacting fermions, such as topological insulators, and discuss how ideas from quantum information, in particular the entanglement spectrum, can be used to characterize them. For topological phases protected by inversion symmetry I argue that this is the ideal tool, and discuss how it leads to a classification of 3D topological phases. Next, I will discuss topological phases that only appear in the presence of interactions, although they share essential characteristics with non-interacting topological phases. A general theory of such states of bosons in 2+1 dimensions will be given, and specific examples, the bosonic analogs of topological superconductors and insulators, will be discussed.
Entanglement, Holography, and the Quantum Phases of Matter

Subir Sachdev Harvard University

July 13, 2012

PIRSA:12070010
Entangling Superconductivity and antiferromagnetism: Quantum Monte Carlo without the sign Problem

Subir Sachdev Harvard University
July 11, 2012

PIRSA:12070009
Condensed Matter
It has long been known that a metal near an instability to antiferromagnetism also has a weak-coupling Cooper instability to spin-singlet d-wave-like superconductivity. However, the theory of the antiferromagnetic quantum critical point flows to strong-coupling in two spatial dimensions, and so the fate of the superconductivity has also been unclear. I will describe a method to realize the generic antiferromagnetic quantum critical in a metal in a sign-problem-free Monte Carlo simulation. Results showing Fermi surface reconstruction and unconventional spin-singlet superconductivity across the critical point are obtained.
Pyrochlore Material Yb_2Ti_2O_7: A Model Quantum Spin Ice
June 15, 2012

PIRSA:12060072
Condensed Matter
We discuss the thermodynamic properties of the model exchange quantum spin ice material Yb_2Ti_2O_7. Using exchange parameters recently determined from high-field neutron scattering measurements, we calculate the thermodynamic properties of this model system. We find very good agreement with the heat capacity, entropy and magnetization measurements on the materials. We show that, in the weak quantum regime, quantum fluctuations lead to the selection, within the spin-ice manifold, of a conventional ordered ground state. However, the excitations above the ground state and their dynamics remain highly non-trivial. They consist of weakly bound spinon-antispinon pairs separated by long strings. We present several pieces of indirect evidence that the low temperature phase transition observed in these materials is to this conventional ordered state.
Relaxation in Driven Integer Quantum Hall Edge States

John Chalker University of Oxford
June 01, 2012

PIRSA:12060000
Mathematical physics
This talk will be about non-equilibrium many-body physics in integer quantum Hall edge states far from equilibrium. Recent experiments have generated a highly non-thermal electron distribution by bringing together at a point contact two quantum Hall edge states originating from sources at different potentials. The relaxation of this distribution to a stationary form is observed as a function of distance downstream from the contact [Phys. Rev. Lett. 105, 056803 (2010)]. I will discuss the broader context for the experiments and a physical picture of the equilibration process. I will also present an exact treatment of a minimal model for the experiment with results that account well for the observations. [Joint work with Dmitry Kovrizhin]

Title	Speaker(s)	Date	Talk Type	Info
Effect of thermal fluctuations in topological p-wave superconductors	Bela Bauer	2012-09-21	Scientific Series	View details
Hamiltonian Theory of Fractional Chern Bands	Ramamurti Shankar	2012-09-14	Scientific Series	View details
Charge fractionalization and entanglement entropy for compressible phases in holography	Liza Huijse	2012-09-11	Scientific Series	View details
Multiplets in the Entanglement Spectrum	Ari Turner	2012-09-06	Scientific Series	View details
Topological Order in Spin Systems	Paul Fendley	2012-08-10	Scientific Series	View details
Glass: The Cinderella Problem of Condensed Matter Physics	Anthony Leggett	2012-08-03	Scientific Series	View details
Integer Quantum Hall Effect for Bosons: A Physical Realization	Senthil Todadri	2012-07-27	Scientific Series	View details
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects	Ashvin Vishwanath	2012-07-27	Scientific Series	View details
Entanglement, Holography, and the Quantum Phases of Matter	Subir Sachdev	2012-07-13	Scientific Series	View details
Entangling Superconductivity and antiferromagnetism: Quantum Monte Carlo without the sign Problem	Subir Sachdev	2012-07-11	Scientific Series	View details
Pyrochlore Material Yb_2Ti_2O_7: A Model Quantum Spin Ice		2012-06-15	Scientific Series	View details
Relaxation in Driven Integer Quantum Hall Edge States	John Chalker	2012-06-01	Scientific Series	View details

Quantum Matter

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