Quantum Matter

436 talks

S021

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Displaying 361 - 372 of 436

Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter
Searching for topological phases in transition metal oxide heterostructures

Ying Ran Boston College
January 31, 2013

PIRSA:13010113
Condensed Matter
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter
Field-induced thermal transport in BEC antiferromagnets

Alexander Chernyshev University of California, Irvine
January 08, 2013

PIRSA:13010002
Condensed Matter
Fermionic toric code model and a new class of topological phases in interacting fermion system

Zheng-Cheng Gu Chinese University of Hong Kong
December 14, 2012

PIRSA:12120037
Condensed Matter
Amplitude mode of the d-density wave state and its relevance to high-Tc cuprates

Ipsita Mandal Shiv Nadar University
November 30, 2012

PIRSA:12110089
Condensed Matter
Beyond the Search for Majorana

Yi-Zhuang You University of California, San Diego
November 30, 2012

PIRSA:12110088
Condensed Matter
Universal driven dynamics near phase transitions : Kibble-Zurek ramps with and without an order parameter

Anushya Chandran Perimeter Institute for Theoretical Physics
November 29, 2012

PIRSA:12110095
Condensed Matter
Fractional quantum Hall effect and tunable interactions

Zlatko Papic University of Leeds
November 29, 2012

PIRSA:12110081
Condensed Matter
Fractional Chern Insulators

Titus Neupert ETH Zurich
November 29, 2012

PIRSA:12110080
Condensed Matter
Dyon condensation in topological Mott insulators

Gil Young Cho Pohang University of Science and Technology
November 28, 2012

PIRSA:12110087
Condensed Matter

Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
We have used a recently proposed quantum Monte Carlo algorithm [1] to study spinons (emergent S = 1/2 excitations) in 2D Resonating-Valence-Bond (RVB) spin liquids and in a J-Q model hosting a Neel – Valence Bond Solid (VBS) phase transition at zero temperature [2]. We confirm that spinons are well defined quasi-particles with finite intrinsic size in the RVB spin liquid. The distance distribution between two spinons shows signatures of deconfinement.
However, at the Neel–VBS transition, we found that the size of a single spinon is significantly greater than the bound-state in VBS, which indicates that spinons are “soft” and shrink when bound state is formed. Both spinon size and confinement length diverge as the critical point is approached. We have also compared spinon statistics in J-Q model with bilayer Heisenberg model and 1D spin chain. We conclude that the spinon deconfinement is marginal in the lowest-energy state in the spin-1 sector, due to very weak attractive spinon interactions. Deconfinement in the vicinity of the critical point should occur at higher energies.
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter
Two types of topological phases have attracted a lot of attention in condensed matter physics: symmetry protected topological(SPT) phases and topologically ordered phases. On the one hand, SPT phases are protected by given global symmetries while there is no topological order in the bulk. On the other hand, topologically ordered phases do not require symmetry and feature topological ground state degeneracy. In this talk, I present a classification of phases with both topological orders and global symmetries, equipped with local bosonic exactly solvable models. This classification, in some sense, organizes previous pieces of understandings on SPT phases, topological orders, symmetry fractionalizations, into a single framework. Solution of the exactly solvable models and measurable consequences will be discussed.
Searching for topological phases in transition metal oxide heterostructures

Ying Ran Boston College
January 31, 2013

PIRSA:13010113
Condensed Matter
In this talk I will present our recent investigations on possible topological phases in (111) heterostructures of transition metal oxide. These (111) heterstructures are promising systems to realize many 2D topological phases at high temperatures, even with strong correlations, which is hard to be achieved in conventional materials. Several examples will be discussed, including high-temperature quantum spin hall effect in LaAlO3/LaAuO3/LaAlO3 bilayer, correlation induced topological phases in LaAlO3/LaNiO3/LaAlO3 multilayer, nearly flat topological band with C=2 (C: Chern number) in SrIrO3 trilayer, and abelian/nonabelian fractional quantum hall effects in the absence of Landau levels (fractional Chern insulators). If time is allowed, I will also briefly introduce our work on classifying wavefunctions of fractional Chern/topological insulators.
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter
Using quantum Monte Carlo simulations, we investigate the finite-temperature phase diagram of hard-core bosons (XY model) in two- and three-dimensional square lattices. To determine the phase boundaries, we perform a finite-size scaling analysis of the condensate fraction and/or the superfluid stiffness. We then discuss how this diagrams can be measured in experiments with trapped ultracold gases, where the systems are inhomogeneous. For that, we introduce a method based on the measurement of the zero-momentum occupation, which is adequate for experiments dealing with both homogeneous and trapped systems. Finally, we provide an analytical argument that demonstrates that the Bose-Hubbard model does not exhibit ﬁnite-temperature BEC in two dimensions, provided that density remains finite across the entire system in the thermodynamic limit.
Field-induced thermal transport in BEC antiferromagnets

Alexander Chernyshev University of California, Irvine
January 08, 2013

PIRSA:13010002
Condensed Matter
Recent experiments in BEC quantum magnets exhibit a dramatic evolution of the thermal conductivity of these materials in magnetic field. By considering various relaxation mechanisms of bosonic excitations in the vicinity of the BEC quantum-critical point at finite temperature we provide a detailed explanation of several unusual features of the data. We identify the leading impurity-scattering interaction and demonstrate that its renormalization due to quantum fluctuations of the paramagnetic state compensates the related mass renormalization effect. This explains the enigmatic absence of the asymmetry between the two critical points in the low-T thermal conductivity data, while such an asymmetry is prominent in many other physical quantities. The observed characteristic "migration'' of the peak in thermal conductivity away from the transition points as a function of temperature is explained as due to a competition between an increase in the number of heat carriers and an enhancement of their mutual scattering. An important role of the three-boson scattering processes within the ordered phase of these systems is also discussed. Other qualitative and quantitative features of the experiment are clarified and the future directions are sketched.
Fermionic toric code model and a new class of topological phases in interacting fermion system

Zheng-Cheng Gu Chinese University of Hong Kong
December 14, 2012

PIRSA:12120037
Condensed Matter
Amplitude mode of the d-density wave state and its relevance to high-Tc cuprates

Ipsita Mandal Shiv Nadar University
November 30, 2012

PIRSA:12110089
Condensed Matter
We study the spectrum of the amplitude mode, the analog of the Higgs mode in high energy physics, for the d-density wave (DDW) state proposed to describe the anomalous phenomenology of the pseudogap phase of the high Tc cuprates. Even though the state breaks translational symmetry by a lattice spacing and is described by a particle-hole singlet order parameter at the wave vector q = Q = (pi, pi), remarkably, we find that the amplitude mode spectrum can have peaks at both q = (0, 0) and q = Q = (pi , pi). In general, the spectra is non-universal, and, depending on the microscopic parameters, can have one or two peaks in the Brillouin zone, signifying confluence of two kinds of magnetic excitations. In light of the recent unexpected observations of multiple magnetic excitations in the pseudogap phase our theory sheds important light on how multiple inelastic neutron peaks at different wave vectors can arise even with an order parameter that condenses at Q = (pi, pi). [Reference: arXiv:1207.6834]
Beyond the Search for Majorana

Yi-Zhuang You University of California, San Diego
November 30, 2012

PIRSA:12110088
Condensed Matter
The search for Majorana zero-modes in condensed matter system has attract increasing research interests recently. Looking for Majorna zero-mode is actually looking for topologically protected ground state degeneracy. The topological degeneracies on closed manifolds have been used to discover/define topological order in many-body systems, which contain excitations with fractional statistics. In this talk, I will present our recent work on new types of topological degeneracy induced by condensing anyons along a line in 2D topological ordered states. Such topological degeneracy can be viewed as carried by each end of the line-defect, which is a generalization of Majorana zero-modes. The ends of line-defects carry projective non-Abelian statistics even though they are produced by condensation of Abelian anyons, and braiding them allow us to perform fault tolerant quantum computations.
Universal driven dynamics near phase transitions : Kibble-Zurek ramps with and without an order parameter

Anushya Chandran Perimeter Institute for Theoretical Physics
November 29, 2012

PIRSA:12110095
Condensed Matter
Near a critical point, the equilibrium relaxation time of a system diverges and any change of control parameters leads to non-equilibrium behavior. The Kibble-Zurek (KZ) problem is to determine
the evolution of the system when the change is slow. In this talk, I will introduce a non-equilibrium scaling limit in which these evolutions are universal and define a KZ universality classification with exponents and scaling functions. I will illustrate the physics accessible in this
scaling limit in simple classical and quantum model theories with symmetry-breaking transitions.

I will then turn to the KZ problem near quantum phase transitions without a local order parameter.
First, I will introduce the necessary background through the example of the Ising gauge theory/generalized toric code. Using duality and the scaling theory developed in the first part of the talk, I will then argue that the late time dynamics exhibits a slow coarsening of the string-net
that is condensed in the starting topologically ordered state. I will also discuss a time dependent amplification of the energy splitting between topologically degenerate states on closed manifolds and the dangerous irrelevance of gapped modes. Finally, I will extend these ideas to the non-abelian SU(2)_k ordered phases of the relevant Levin-Wen models.
Fractional quantum Hall effect and tunable interactions

Zlatko Papic University of Leeds
November 29, 2012

PIRSA:12110081
Condensed Matter
In this talk I will review some existing experimental methods, as well as a few recent theoretical proposals, to tune the interactions in a number of low-dimensional systems exhibiting the fractional quantum Hall effect (FQHE). The materials in question include GaAs wide quantum wells and multilayer graphene, where the tunability of the electron-electron interactions can be achieved via modifying the band structure, dielectric environment of the sample, by tilting the magnetic field or varying the mass tensor, and by mixing of electronic subbands and Landau levels. Because the interesting topological (and in particular, non-Abelian) states arise solely due to strong interactions, the ability to tune them is essential for ``designing" more robust FQHE states. Furthermore, I will argue that some of these mechanisms can also be used to probe the subtle aspects of FQHE physics, such as the breaking of particle-hole symmetry between the Moore-Read Pfaffian and anti-Pfaffian states, and the transition between FQHE fluids and broken-symmetry states due to the fluctuation of the intrinsic geometric degree of freedom.
Fractional Chern Insulators

Titus Neupert ETH Zurich
November 29, 2012

PIRSA:12110080
Condensed Matter
Fractional Chern insulators (FCIs) are topologically ordered states of interacting fermions that share their universal properties with fractional quantum Hall states in Landau levels. FCIs have been found numerically in a variety of two-dimensional lattice models upon partially filling an almost dispersionless band with nontrivial topological character with repulsively interacting fermions. I will show how FCIs emerge in bands with Chern number C=1 and C=2 and in Z_2 topological insulators, where the latter are accompanied by a spontaneous breaking of time-reversal symmetry. Further, I will discuss the relevance of the noncommutative quantum geometry of the flat topological band to the stability of FCIs and how they can be distinguished from phases of spontaneously broken point group symmetry, such as charge density waves.
Dyon condensation in topological Mott insulators

Gil Young Cho Pohang University of Science and Technology
November 28, 2012

PIRSA:12110087
Condensed Matter
We consider quantum phase transitions out of topological Mott insulators in which the ground state of the fractionalized excitations (fermionic spinons) is topologically non-trivial. The spinons in topological Mott insulators are coupled to an emergent compact U(1) gauge field with a so-called "axion" term. We study the confinement transitions from the topological Mott insulator to broken symmetry phases, which may occur via the condensation of dyons. Dyons carry both "electric" and "magnetic" charges, and arise naturally in this system because the monopoles of the emergent U(1) gauge theory acquires gauge charge due to the axion term. It is shown that the dyon condensate, in general, induces simultaneous current and bond orders. When the magnetic transition is driven by dyon condensation, we identify the bond order as valence bond solid order and the current order as scalar spin chirality order. Hence, the confined phase of the topological Mott insulator is an exotic phase where the scalar spin chirality and the valence bond order coexist and appear via a single transition. If time allows, I will also discuss our recent work on the proximate symmetry-broken phases of Z2 spin liquid on Kagome lattice.

Title	Speaker(s)	Date	Talk Type	Info
Looking for spinon deconfinement in two dimensions	Ying Tang	2013-02-05	Scientific Series	View details
A classification of symmetry enriched topological phases with exactly solvable models	Ying Ran	2013-02-01	Scientific Series	View details
Searching for topological phases in transition metal oxide heterostructures	Ying Ran	2013-01-31	Scientific Series	View details
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.	Juan Carrasquilla	2013-01-22	Scientific Series	View details
Field-induced thermal transport in BEC antiferromagnets	Alexander Chernyshev	2013-01-08	Scientific Series	View details
Fermionic toric code model and a new class of topological phases in interacting fermion system	Zheng-Cheng Gu	2012-12-14	Scientific Series	View details
Amplitude mode of the d-density wave state and its relevance to high-Tc cuprates	Ipsita Mandal	2012-11-30	Scientific Series	View details
Beyond the Search for Majorana	Yi-Zhuang You	2012-11-30	Scientific Series	View details
Universal driven dynamics near phase transitions : Kibble-Zurek ramps with and without an order parameter	Anushya Chandran	2012-11-29	Scientific Series	View details
Fractional quantum Hall effect and tunable interactions	Zlatko Papic	2012-11-29	Scientific Series	View details
Fractional Chern Insulators	Titus Neupert	2012-11-29	Scientific Series	View details
Dyon condensation in topological Mott insulators	Gil Young Cho	2012-11-28	Scientific Series	View details

Quantum Matter

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