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Condensed Matter

This series consists of talks in the area of Condensed Matter.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.


Jeudi nov 29, 2012

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

Scientific Areas: 


Jeudi nov 29, 2012

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

Scientific Areas: 


Mercredi nov 28, 2012

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

Scientific Areas: 


Mardi nov 27, 2012

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

Scientific Areas: 


Mardi nov 27, 2012

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



Mercredi nov 21, 2012
Scientific Areas: 


Vendredi nov 16, 2012

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

Scientific Areas: 


Vendredi oct 26, 2012

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

Scientific Areas: 


Mardi oct 23, 2012


Topological gauge theories and group cohomology

Robbert Dijkgraaf and Edward Witten


Braiding statistics approach to symmetry-protected topological phases

Michael Levin, Zheng-Cheng Gu

Scientific Areas: 


Vendredi oct 19, 2012

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

Scientific Areas: