Quantum Matter

Displaying 337 - 348 of 438

Topological States in Strongly-Correlated Materials

Kai Sun University of Michigan–Ann Arbor
November 15, 2013

PIRSA:13110082
Condensed Matter
Z2 spin liquid in kagome Heisenberg antiferromagnet

Yuan Wan Chinese Academy of Sciences
November 05, 2013

PIRSA:13110086
Condensed Matter
Silicene - a Wonder Electron Carpet

Baskaran Ganapathy Institute of Mathematical Sciences
October 29, 2013

PIRSA:13100128
Condensed Matter
Wilsonian and large N approaches to non-Fermi liquids

Shamit Kachru Stanford University
October 22, 2013

PIRSA:13100109
Condensed Matter
Geometry of quantum phases and emergent Newtonian dynamics

Anatoli Polkovnikov Boston University
October 15, 2013

PIRSA:13100083
Condensed Matter
Fractional solitons on the edge of the Fractional Quantum Hall states

Paul Wiegmann University of Chicago - James Franck Institute
October 10, 2013

PIRSA:13100073
Condensed Matter
Geometry and Topology in the Fractional Quantum Hall Effect

Duncan Haldane Princeton University
October 07, 2013

PIRSA:13100086
Condensed Matter
Self-organized topological state with Majorana fermions

Marcel Franz University of British Columbia
September 17, 2013

PIRSA:13090071
Condensed Matter
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Wavelets and MERA

Steven White University of California, Irvine
August 30, 2013

PIRSA:13080057
Condensed Matter
Interacting topological insulators in three dimensions: classification and properties

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 20, 2013

PIRSA:13080055
Condensed Matter
Models of Interacting Topological Phases

Scott Geraedts California Institute of Technology
June 25, 2013

PIRSA:13060010
Condensed Matter

Topological States in Strongly-Correlated Materials

Kai Sun University of Michigan–Ann Arbor
November 15, 2013

PIRSA:13110082
Condensed Matter
In the study of strongly-correlated insulators, a long-standing puzzle remained open for over 40 years. Some Kondo insulators (or mixed-valent insulators) display strange electrical transport that cannot be understood if one assumes that it is governed by the three-dimensional bulk. In this talk, I show that some 3D Kondo insulators have the right ingredients to be topological insulators, which we called “topological Kondo insulators”. For a topological Kondo insulator, the low-temperature transport is dominated by the 2D surface rather than the 3D bulk, because the bulk of this material is an insulator while its surface is a topologically-protected 2D metal. This theoretical picture offers a natural explanation for the long-standing puzzle mentioned above. In addition, we also find that Kondo insulators can support another type of nontrivial topological structure protected by lattice symmetries, which we called “topological crystalline Kondo insulators”. In particular, we predict that SmB$_6$ is both a topological Kondo insulator and a topological crystalline Kondo insulator and I will also discuss recent experiments, which reveal the surface states in SmB$_6$.
Z2 spin liquid in kagome Heisenberg antiferromagnet

Yuan Wan Chinese Academy of Sciences
November 05, 2013

PIRSA:13110086
Condensed Matter
A quantum spin liquid is a hypothesized ground state of a magnet without long-range magnetic order. Similar to a liquid, which is spatially uniform and strongly correlated, a quantum spin liquid preserves all the symmetries and exhibits strong correlations between spins. First proposed by P. W. Anderson in 1973, it has remained a conjecture until recently. In the past couple of years, numerical studies have provided strong evidences for quantum spin liquid in a simple model, the kagome Heisenberg antiferromagnet. In this talk, I will describe a low-energy effective theory for this magnet in terms of a lattice gauge theory with the simplest possible mathematical structure (a group of two elements, namely Z2). I will show that the theory reproduces many characteristic features observed numerically, thereby providing a bridge between the numeircs and the analytics. Furthermore, I will present theoretical predictions which could be tested in future numerical studies.
Silicene - a Wonder Electron Carpet

Baskaran Ganapathy Institute of Mathematical Sciences
October 29, 2013

PIRSA:13100128
Condensed Matter
Graphene is a 2 dimensional net of strongly bonded carbon atoms. This magic carpet has taken us to new heights in the last decade. Silicene and Germanene are analogue nets, made of silicon and germanium atoms respectively, but with a relatively weaker chemical bond. I will argue that these carpets perform some new tricks by not being a carbon copy of graphene. We have suggested [1] that silicene and germanene are Mott insulators and potential abode for room temperature superconductivity, quantum spin liquids and more
Wilsonian and large N approaches to non-Fermi liquids

Shamit Kachru Stanford University
October 22, 2013

PIRSA:13100109
Condensed Matter
We use Wilsonian RG and large N techniques to study the quantum field theory of a critical boson interacting with a Fermi surface, and compare/contrast the results with those coming from holography.
Geometry of quantum phases and emergent Newtonian dynamics

Anatoli Polkovnikov Boston University
October 15, 2013

PIRSA:13100083
Condensed Matter
In the first part of this talk I will discuss how one can characterize geometry of quantum phases and phase transitions based on the Fubini-Study metric, which characterizes the distance between ground state wave-functions in the external parameter space. This metric is closely related to the Berry curvature. I will show that there are new geometric invariants based on the Euler characteristic. I will also show how one can directly measure this metric tensor in simple dynamical experiments. In the second part of the talk I will discuss emergent nature of macroscopic equations of motion (like Newton's equations) showing that they appear in the leading order of non-adiabatic expansion. I will show that the Berry curvature gives the Coriolis force and the Fubini-Study metric tensor is closely related to the inertia mass. Thus I will argue that any motion (not necessarily motion in space) is geometrical in nature.
Fractional solitons on the edge of the Fractional Quantum Hall states

Paul Wiegmann University of Chicago - James Franck Institute
October 10, 2013

PIRSA:13100073
Condensed Matter
We argue that dynamics of gapless Fractional Quantum Hall Edge states is essentially non-linear and that it features fractionally quantized solitons propagating along the edge. Observation of solitons would be a direct evidence of fractional charges. We show that the non-linear dynamics of the Laughlin's FQH state is governed by the quantum Benjamin-Ono equation.
Geometry and Topology in the Fractional Quantum Hall Effect

Duncan Haldane Princeton University
October 07, 2013

PIRSA:13100086
Condensed Matter
The FQHE is exhibited by electrons moving on a 2D surface through which a magnetic flux passes, giving rise to flat bands with extensive degeneracy (Landau levels). The degeneracy of a partially-filled Landau level is lifted by Coulomb repulsion between the electrons, which at certain rational fillings, leads to gapped incompressible topologically-ordered fluid states exhibiting the FQHE. Successful model wavefunctions for FQHE states, such as the Laughlin and Moore-Read states, are surprisingly related to Euclidean conformal field theory, even though they are gapped incompressiible quantum fluids with a fundamental unit of area set by the area per magnetic flux quantum h/e. The model wavefunctions are parametrized by a continuously-variable Euclidean metric, just like the Euclidean conformal group of the cft to which they are related. This metric is fixed locally both by the form of the projected Coulomb interaction within the partially-filled Landau level, and by local gradients of the tangential electric field on the 2D surface, promoting it from a static flat metric fixed globally by the cft, to a dynamic local physical degree of freedom of the FQHE fluid with area-preserving zero-point fluctuations that leave an imprint in the ground-state structure function. The curious connection to cft appears to be that the Virasoro algebra plays a fundament role in both cft and FQHE, for apparently-unrelated reasons. In the FQHE it derives from a chiral "gravitional" (geometric) topologically-protected anomaly at the edge of the fluid that is also revealed in the entanglement spectrum of a cut through the bulk fluid.
Self-organized topological state with Majorana fermions

Marcel Franz University of British Columbia
September 17, 2013

PIRSA:13090071
Condensed Matter
Topological phases, quite generally, are difficult to come by. They either occur under rather extreme conditions (e.g. the quantum Hall liquids, which require high sample purity, strong magnetic fields and low temperatures) or demand fine tuning of system parameters, as in the majority of known topological insulators. Many perfectly sensible topological phases, such as the Weyl semimetals and topological superconductors, remain experimentally undiscovered. In this talk I will introduce a system in which a key dynamical parameter adjusts itself in response to the changing external conditions so that the ground state naturally favors the topological phase. The system consists of a quantum wire formed of individual magnetic atoms placed on the surface of an ordinary s-wave superconductor. It realizes the Kitaev paradigm of topological superconductivity when the wavevector characterizing the emergent spin helix dynamically self-tunes to support the topological phase.
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Wavelets and MERA

Steven White University of California, Irvine
August 30, 2013

PIRSA:13080057
Condensed Matter
Some of the key insights that led to the development of DMRG stemmed from studying the behavior of real space RG for single particle wavefunctions, a much simpler context than the many-particle case of main interest. Similarly, one can gain insight into MERA by studying wavelets. I will introduce basic wavelet theory and show how one of the most well-known wavelets, a low order orthogonal wavelet of Daubechies, can be realized as the fixed point of a specific MERA (in single-particle direct-sum space). Higher order wavelets and the conflict between compactness in real and Fourier space may provide insight into generalized MERAs for many particle systems.
Interacting topological insulators in three dimensions: classification and properties

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 20, 2013

PIRSA:13080055
Condensed Matter
A fundamental open problem in condensed matter physics is how the dichotomy between conventional and topological band insulators is modified in the presence of strong electron interactions. In this talk I describe recent work showing that there are 6 new electronic topological insulators that have no non-interacting counterpart. Combined with the previously known band-insulators, these produce a total of 8 topologically distinct phases. Two of the new topological insulators have a simple physical description as Mott insulators in which the electron spins form spin analogs of the familiar topological band-insulator. The remaining are obtained as combinations of these two `topological paramagnets' and the topological band insulator. These 8 phases form a complete list of all possible interacting topological insulators, and are classified by a $\mathbb{Z}_2^3$ group-structure. As a necessary part of the talk I will also review progress in the theory of bosonic Symmetry Protected Topological phases in 3d.
Models of Interacting Topological Phases

Scott Geraedts California Institute of Technology
June 25, 2013

PIRSA:13060010
Condensed Matter
We present a set of models which realize interacting topological phases. The models are constructed in 2 dimensions for a system with U(1)xU(1) symmetry. We demonstrate that the models are topological by measuring their Hall conductivity, and demonstrating that they have gapless edge modes. We have also studied the models numerically.

Title	Speaker(s)	Date	Talk Type	Info
Topological States in Strongly-Correlated Materials	Kai Sun	2013-11-15	Scientific Series	View details
Z2 spin liquid in kagome Heisenberg antiferromagnet	Yuan Wan	2013-11-05	Scientific Series	View details
Silicene - a Wonder Electron Carpet	Baskaran Ganapathy	2013-10-29	Scientific Series	View details
Wilsonian and large N approaches to non-Fermi liquids	Shamit Kachru	2013-10-22	Scientific Series	View details
Geometry of quantum phases and emergent Newtonian dynamics	Anatoli Polkovnikov	2013-10-15	Scientific Series	View details
Fractional solitons on the edge of the Fractional Quantum Hall states	Paul Wiegmann	2013-10-10	Scientific Series	View details
Geometry and Topology in the Fractional Quantum Hall Effect	Duncan Haldane	2013-10-07	Scientific Series	View details
Self-organized topological state with Majorana fermions	Marcel Franz	2013-09-17	Scientific Series	View details
Edge states at domain wall junctions in supersymmetric gauge theory	Davide Gaiotto	2013-09-13	Scientific Series	View details
Wavelets and MERA	Steven White	2013-08-30	Scientific Series	View details
Interacting topological insulators in three dimensions: classification and properties	Senthil Todadri	2013-08-20	Scientific Series	View details
Models of Interacting Topological Phases	Scott Geraedts	2013-06-25	Scientific Series	View details

Quantum Matter

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