Quantum Matter

431 talks

S021

Collection Type

Series

Subject

Condensed Matter

Displaying 325 - 336 of 431

The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng
California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter
Paying the price of naturalness with a supersymmetric twin Higgs

Kiel Howe
Stanford University
January 21, 2014

PIRSA:14010105
Condensed Matter
A lattice non-perturbative definition of chiral fermion/gauge theory from Topological Order

Juven Wang
Harvard University
December 13, 2013

PIRSA:13120069
Condensed Matter
Symmetry Enriched Quantum Spin Ices On the Pyrochlore Lattice

Gang Chen
Fudan University
December 06, 2013

PIRSA:13120055
Condensed Matter
The Amplitude Mode in Condensed Matter : Higgs Hunting on a Budget

Daniel Arovas
University of California, San Diego
November 19, 2013

PIRSA:13110054
Condensed Matter
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 College
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

The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng
California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter
The quantum spin liquid is an emergent new state of matter, which has attracted a lot of recent attention. In particular, the time reversal symmetry broken spin liquid (Kalmeyer et. al. and Wen et. al.), characterized by the chiral ordering and fractionalized quasi-particle as a realization of the fractional quantum Hall state had been proposed for more than 20 years, but never identified as the true ground state in any more generic (e.g. Heisenberg spin exchange) models with time reversal symmetry. Here I will report two concrete examples where chiral spin liquid (CSL) emerge for a range of parameter space for kagome J1-J2-J3 (three nearest neighbors) model based on accurate density matrix renormalization group (DMRG) simulations. We identify long-range chiral ordering, ground state degeneracy, characteristic entanglement spectra, and the fractionalized topological Chern number to establish the topological state in such a system as the long-sought CSL. We further explicitly extract the modular matrix, which captures all the information of the fractional statistics of the quasi-particles in the system. I will also discuss the close relation of our model to some frustrated kagome antiferromagnets, and make a conjecture that J1 kagome model is near an unconventional critical point. I will conclude the talk with some discussions of the open directions.
Paying the price of naturalness with a supersymmetric twin Higgs

Kiel Howe
Stanford University
January 21, 2014

PIRSA:14010105
Condensed Matter
What is the price of naturalness? In minimal extensions of the standard model, stringent limits on new colored particles and measurements of Higgs properties from the LHC severely challenge the hypothesis of naturalness of the electroweak scale. However, these measurements also provide unprecedented guidance in exploring non-minimal models of new electroweak physics. The supersymmetric twin Higgs provides a concrete example where few-percent level tuning remains compatible with superpartner limits and Higgs physics as well as gauge coupling unification and other successes of the MSSM. Studying such models in detail is crucial to understanding the role naturalness will play as a motivating principle for future searches at the 13 TeV LHC and beyond.
A lattice non-perturbative definition of chiral fermion/gauge theory from Topological Order

Juven Wang
Harvard University
December 13, 2013

PIRSA:13120069
Condensed Matter
A non-perturbative definition of anomaly-free chiral fermions and bosons in 1+1D spacetime as finite quantum systems on 1D lattice is proposed. In particular, any 1+1D anomaly-free chiral matter theory can be defined as finite quantum systems on 1D lattice with on-site symmetry, if we include strong interactions between matter fields. Our approach provides another way, apart from Ginsparg-Wilson fermions approach, to avoid the fermion-doubling challenge. In general, using the defining connection between gauge anomalies and the symmetry-protected topological orders, we propose that any truly anomaly-free chiral gauge theory can be non-perturbatively defined by putting it on a lattice in the same dimension. As an additional remark, we conjecture/prove the equivalence relation between 't Hooft anomaly matching conditions and the boundary fully gapping rules.
Symmetry Enriched Quantum Spin Ices On the Pyrochlore Lattice

Gang Chen
Fudan University
December 06, 2013

PIRSA:13120055
Condensed Matter
Quantum spin liquid (QSL) is an exotic phase of matter and provides an interesting example of emergent non-locality. Even though many materials have been proposed as candidates for QSLs, there is no direct confirmation of QSLs in any of these systems. Quantum spin ice (QSI) is a physical realization of U(1) QSLs on the pyrochlore lattice. We consider a class of electron systems in which dipolar-octupolar Kramers doublets arise on the pyrochlore lattice. In the localized limit, the Kramers doublets are described by the effective spin 1/2 pseudospins. The most general nearest-neighbor exchange model between these pseudospins is the XYZ model. We show that this XYZ model exhibit two distinct symmetry enriched QSI phases, that we dub dipolar QSI and octupolar QSI. This XYZ model is absent from the notorious sign problem for a quantum Monte Carlo simmulation. We also discuss the potential relevance to real material systems.
The Amplitude Mode in Condensed Matter : Higgs Hunting on a Budget

Daniel Arovas
University of California, San Diego
November 19, 2013

PIRSA:13110054
Condensed Matter
The amplitude mode is a ubiquitous phenomenon in systems with broken continuous symmetry and effective relativistic dynamics, and has been observed in magnets, charge density waves, cold atom systems, and superconductors. It is a simple analog of the Higgs boson of particle physics. I will discuss the properties of the amplitude mode and its somewhat surprising visibility in two-dimensional systems, recently confirmed in cold atom experiments. The behavior in the vicinity of a quantum critical point will be stressed, comparing theoretical, numerical, and experimental results.
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 College
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.

Title	Speaker(s)	Date	Talk Type	Info
The emergent of the chiral spin liquid in kagome Heisenberg model	Dong-Ning Sheng	2014-02-20	Scientific Series	View details
Paying the price of naturalness with a supersymmetric twin Higgs	Kiel Howe	2014-01-21	Scientific Series	View details
A lattice non-perturbative definition of chiral fermion/gauge theory from Topological Order	Juven Wang	2013-12-13	Scientific Series	View details
Symmetry Enriched Quantum Spin Ices On the Pyrochlore Lattice	Gang Chen	2013-12-06	Scientific Series	View details
The Amplitude Mode in Condensed Matter : Higgs Hunting on a Budget	Daniel Arovas	2013-11-19	Scientific Series	View details
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

Quantum Matter

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