C13035 - PI-UIUC 2013PI-UIUC Joint Workshop On Strongly Correlated Quantum Many-Body Systems
http://pirsa.org/podcast/C13035
Science2020http://blogs.law.harvard.edu/tech/rssen-caSat, 08 Aug 2020 10:57:43 -0400Sat, 08 Aug 2020 10:57:43 -0400G180help@perimeterinstitute.capirsa.org<![CDATA[Hofstadter’s Butterfly and interaction driven quantum Hall ferromagnetism in graphene]]>Electrons moving in a periodic electric potential form Bloch energy
bands where the mass of electrons are effectively changed. In a strong
magnetic field, the cyclotron orbits of free electrons are quantized and
Landau levels forms with a massive degeneracy within. In 1976,
Hofstadter showed that for 2-dimensional electronic system, the
intriguing interplay between these two quantization effects can lead
into a self-similar fractal set of energy spectrum known as
“Hofstadter’s Butterfly.” Experimental efforts to demonstrate this
fascinating electron energy spectrum have continued ever since. Recent
advent of graphene, where its Bloch electrons can be described by Dirac
feremions, provides a new opportunity to investigate this half century
old problem experimentally. In this presentation, I will discuss the
experimental realization Hofstadter’s Butterfly via substrate engineered
graphene under extremely high magnetic fields controlling two competing
length scales governing Dirac-Bloch states and Landau orbits,
respectively. In addition, the strong Coulomb interactions and
approximate spin-pseudo spin symmetry are predicted to lead to a variety
of integer quantum Hall ferromagnetic and fractional quantum Hall
states and the quantum phase transition between them in graphene. I will
discuss several recent experimental evidences to demonstrate the role
of the electron interaction in single and bilayer graphene.]]>Philip Kim
http://streamer2.perimeterinstitute.ca/mp3/13110070.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110070.mp3Thu, 07 Nov 2013 09:05:00 -0500<![CDATA[Unparticles and Fermi Arcs in the Cuprates]]>One of the open problems in strong correlation physics is whether or not
Luttinger's theorem works for doped Mott insulators, particularly in
the pseudo gap regime where the pole-like excitations form only a Fermi
arc. I will begin this talk by using this theorem to count particles and
show that it fails in general for the Mott state. The failure stems
from the divergent self energy that underlies Mottness. When such a
divergence is present, charged degrees of freedom are present that have
no particle interpretation. I will argue that such excitations are
governed by a non-trivial IR fixed point and the propagator of which is
of the unparticle form proposed by Georgi. I will show how a gravity
dual can be used to determine the scaling dimension of the unparticle
propagator. I will close by elucidating a possible superconducting
instability of unparticles and demonstrate that unparticle stuff is
likely to display fractional statistics in the dimensionalities of
interest for strongly correlated electron matter. Time permitting, an
underlying theory of the strongly coupled fixed point will be outlined.]]>Philip Phillips
http://streamer2.perimeterinstitute.ca/mp3/13100131.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13100131.mp3Thu, 07 Nov 2013 10:45:00 -0500<![CDATA[Entanglement at strongly-interacting quantum critical points]]>At a quantum critical point (QCP) in two or more spatial dimensions,
leading-order contributions to the scaling of entanglement entropy
typically follow the "area" law, while sub-leading behavior contains
universal physics. Different universal functions can be access through
entangling subregions of different geometries. For example, for
polygonal shaped subregions, quantum field theories have demonstrated
that the sub-leading scaling is logarithmic, with a universal
coefficient dependent on the number of vertices in the polygon.
Although such universal quantities are routinely studied in
non-interacting field theories, it requires numerical simulation to
access them in interacting theories. In this talk, we discuss numerical
calculations of the Renyi entropies at QCPs in 2D quantum lattice
models. We calculate the universal coefficient of the vertex-induced
logarithmic scaling term, and compare to non-interacting field theory
calculations. Also, we examine the shape dependence of the Renyi
entropy for finite-size lattices with smooth subregion boundaries. Such
geometries provide a sensitive probe of the gapless wavefunction in the
thermodynamic limit, and give new universal quantities that could be
examined by field-theoretical studies in 2+1D.]]>Roger Melko
http://streamer2.perimeterinstitute.ca/mp3/13110071.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110071.mp3Thu, 07 Nov 2013 11:30:00 -0500<![CDATA[Topological Phases in Transition Metal Oxides]]>Certain varieties of transition metal oxides possess both significant
interactions and strong spin-orbit coupling. In this talk I will
describe materials-motivated models that predict topological phases in
heterostructured and bulk transition metal oxides. We find Z2
topological insulators, Chern insulators, topological crystalline
insulators, and interaction-driven topological phases not adiabatically
connected to non-interacting topological phases.]]>Gregory Fiete
http://streamer2.perimeterinstitute.ca/mp3/13110072.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110072.mp3Thu, 07 Nov 2013 14:00:00 -0500<![CDATA[Many-body localization: entanglement, emergent conservation laws, and the structure of eigenstates]]> ]]>Dmitry Abanin
http://streamer2.perimeterinstitute.ca/mp3/13110073.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110073.mp3Thu, 07 Nov 2013 15:00:00 -0500<![CDATA[Quantum quenches & holography]]>We employ holographic techniques to study quantum quenches at finite
temperature, where the quenches involve varying the coupling of the
boundary theory to a relevant operator with an arbitrary conformal
dimension. The evolution of the system is studied by evaluating the
expectation value of the quenched operator and the stress tensor
throughout the process. The time dependence of the new coupling is
characterized by a fixed timescale and the response of the observables
depends on the ratio of the this timescale to the initial temperature.
The observables exhibit universal scaling behaviours when the
transitions are either fast or slow, i.e., when this ratio is very small
or very large. For fast quenches, we uncover a universal scaling
behaviour in the response of the system, which depends only on the
conformal dimension of the quenched operator in the vicinity of the
ultraviolet fixed point of the theory.]]>Robert Myers
http://streamer2.perimeterinstitute.ca/mp3/13110074.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110074.mp3Thu, 07 Nov 2013 16:15:00 -0500<![CDATA[Discussion]]>Eduardo Fradkin
http://streamer2.perimeterinstitute.ca/mp3/13110075.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110075.mp3Thu, 07 Nov 2013 17:00:00 -0500<![CDATA[Majorana State Properties in Semiconductor and Oxide Superconducting Quantum Wires]]>When proximity coupled to s-wave superconductors, quantum wires can
support effective p-wave superconductivity under appropriate
circumstances. The p-wave state has Majorana states at the wire ends
which can store quantum information. I will discuss some properties of
Majorana states formed in oxide and semiconductor quantum wires,
including superconducting state phase diagrams as a function of
spin-orbit coupling strength, Fermi energy, and external magnetic field
strength, and Majorana exchange properties.]]>Allan MacDonald
http://streamer2.perimeterinstitute.ca/mp3/13110076.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110076.mp3Fri, 08 Nov 2013 09:00:00 -0500<![CDATA[Quantum and Classical Anomalies]]>I will begin reviewing the Callan-Harvey mechanism of anomaly inflow
with particular focus on topological edge states and show how the
inflow picture naturally converts the non-covariant "consistent"
gauge anomaly of Bardeen and Zumino to the more physical "covariant"
anomaly. I will then discuss some recent derivations of the covariant
form of the gauge anomaly from classical phase space flows.]]>Michael Stone
http://streamer2.perimeterinstitute.ca/mp3/13110077.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110077.mp3Fri, 08 Nov 2013 10:30:00 -0500<![CDATA[Twist Defects in Topological Systems with Anyonic Symmetries]]>Twist defects are point-like objects that support robust non-local
storage of quantum information and non-abelian unitary operations.
Unlike quantum deconfined anyonic excitations, they rely on symmetry
rather than a non-abelian topological order. Zero energy Majorana bound
states can arise at lattice defects, such as disclinations and
dislocations, in a topological crystalline superconductor. More general
parafermion bound state can appear as twist defects in a topological
phase with an anyonic symmetry, such as a bilayer fractional quantum
Hall state and the Kitaev toric code. They are however fundamentally
different from quantum anyonic excitations in a true topological phase.
This is demonstrated by their unconventional exchange and braiding
behavior, which is characterized by a modified spin statistics theorem
and modular invariance.]]>Jeffrey Teo
http://streamer2.perimeterinstitute.ca/mp3/13110078.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110078.mp3Fri, 08 Nov 2013 11:15:00 -0500<![CDATA[Discussion]]>Xiao-Gang Wen
http://streamer2.perimeterinstitute.ca/mp3/13110079.mp3
Sciencehttp://streamer2.perimeterinstitute.ca/mp3/13110079.mp3Fri, 08 Nov 2013 14:00:00 -0500