Quantum Matter

Displaying 373 - 384 of 439

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
Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012

PIRSA:12110079
Condensed Matter
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012

PIRSA:12110077
Condensed Matter
Superradiant Superconductivity

Baskaran Ganapathy Institute of Mathematical Sciences
November 16, 2012

PIRSA:12110071
Condensed Matter
An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi Stanford University
October 26, 2012

PIRSA:12100051
Condensed Matter
An informal discussion about topological gauge theory

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
October 23, 2012

PIRSA:12100129
Quantum Fields and Strings
Self-localization of a single hole in Mott antiferromagnets

Zheng-Yu Weng Tsinghua University
October 19, 2012

PIRSA:12100077
Condensed Matter

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.
Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
In this talk I will describe my work characterizing quantum entanglement in systems with a Fermi surface. This class includes everything from Fermi liquids to exotic spin liquids in frustrated magnets and perhaps even holographic systems. I review my original scaling argument and then describe in detail a number of new precise results on entanglement in Fermi liquids. I will also discuss recent quantum Monte Carlo calculations of Renyi entropies and will argue that we now have a rather complete agreement between theory and numerics for Fermi liquid entanglement. I will also discuss universal crossovers between thermal and entanglement entropy and a class of solvable interacting models where we can prove the universality of the Widom formula for Fermi surface entanglement. If there is time, I will comment on several other topics including fluctuations of conserved quantities and connections to holography.
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085

Most applications of the density matrix renormalization group (DMRG) have been to lattice models with short range interactions. But recent developments in DMRG technology open the door to studying continuum systems with long-range interactions in one dimension (1d). One key motivation is simulating cold atom experiments, where it is possible to engineer Hamiltonians of precisely this type. We have been applying DMRG in the 1d continuum with another motivation: to investigate and improve density functional theory (DFT). DFT has exact mathematical foundations, but in practice one must use approximations. These approximations work incredibly well for weakly correlated systems yet fail when correlations are strong. Improving DFT directly for realistic 3d systems is hard because few systems can be solved exactly. By working in the 1d continuum instead, we can use the power of DMRG to study DFT. We can implement both the exact DFT formalism and standard DFT approximations. After showing how to overcome the challenges in performing these calculations, I will discuss some of the key questions we are investigating, for example, the ability of DFT to predict gaps of insulating systems.
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012

PIRSA:12110079
Condensed Matter
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012

PIRSA:12110077
Condensed Matter
Superradiant Superconductivity

Baskaran Ganapathy Institute of Mathematical Sciences
November 16, 2012

PIRSA:12110071
Condensed Matter
In Dicke Superradiance, a collection of 2-level atoms interacting with a single boson mode acquires, through quantum coherence, an enhanced emission property and a rich dynamics. We suggest possibility of Dicke superradiance in a BCS superconductor. The necessary 2-level atoms are identified with Anderson pseudo spins seeing a self consistent mean field in k-space. A way to couple these 2-level bose atoms to an external boson mode and create a novel non equilibrium superradiant superconductivity (SRSC) is suggested. Our mechanism offers a hope to realize transient superconductivity, even at room temperatures, in the pseudo gap phase of certain underdoped cuprates. Recent experiments are briefly discussed in this light. Further SRSC exhibits interesting quantum entanglement and superfluorescence properties.
An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132

Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi Stanford University
October 26, 2012

PIRSA:12100051
Condensed Matter
An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field, which are called fractional Chern insulators. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations become non-Abelian defects which create "worm holes" connecting the effective layers, and effectively change the topology of the space. Such topology-changing defects, which we name as "genons", can also be defined in other physical systems. We develop methods to compute the projective non-abelian braiding statistics of the genons, and we find the braiding is given by adiabatic modular transformations, or Dehn twists, of the topological state on the effective genus g surface. We find situations where the > genons have quantum dimension 2 and can be used for universal topological quantum computing (TQC), while the host topological state is by itself non-universal for TQC.
An informal discussion about topological gauge theory

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
October 23, 2012

PIRSA:12100129
Quantum Fields and Strings
Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Self-localization of a single hole in Mott antiferromagnets

Zheng-Yu Weng Tsinghua University
October 19, 2012

PIRSA:12100077
Condensed Matter
Anderson localization - quantum suppression of carrier diffusion due to disorders - is a basic notion of modern condensed matter physics. Here I will talk about a novel localization phenomenon totally contrary to this common wisdom. Strikingly, it is purely of strong interaction origin and occurs without the assistance of disorders. Specifically, by combined numerical (density matrix renormalization group) method and analytic analysis, we show that a single hole injected in a quantum antiferromagnetic ladder is generally self-localized even though the system respects the translational symmetry. The localization length is found to monotonically decrease with the increase of leg number, indicating stronger self-localization in the two-dimensional limit. We find that a peculiar coupling between the doped charge and the quantum spin background causes quantum interference among different hole paths. The latter brings the hole's itinerant motion to a halt, a phenomenological analogy to Anderson localization. Our findings are opposite to the common belief of the quasiparticle picture for the doped hole and unveil a completely new paradigm for lightly doped Mott insulators.

Title	Speaker(s)	Date	Talk Type	Info
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
Entanglement and the Fermi surface	Brian Swingle	2012-11-27	Scientific Series	View details
Exact Calculations in the 1D Continuum for DFT and Beyond		2012-11-27	Scientific Series	View details
Twisted quantum double model of topological phases	Yidun Wan	2012-11-21	Scientific Series	View details
Twisted quantum double model of topological phases	Yidun Wan	2012-11-21	Other	View details
Superradiant Superconductivity	Baskaran Ganapathy	2012-11-16	Scientific Series	View details
An Informal Discussion About Topological Gauge Theory, part 2	Xiao-Gang Wen	2012-10-30	Other	View details
Synthetic non-Abelian anyons in fractional Chern insulators and beyond	Xiaoliang Qi	2012-10-26	Scientific Series	View details
An informal discussion about topological gauge theory	Xiao-Gang Wen	2012-10-23	Scientific Series	View details
Self-localization of a single hole in Mott antiferromagnets	Zheng-Yu Weng	2012-10-19	Scientific Series	View details

Quantum Matter

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