This series consists of talks in the area of Condensed Matter.
Much effort has been devoted to the study of systems with
topological order, motivated by practical issues as well as more field
theoretical and mathematical concerns. This talk will give an overview of some
of the field, describing abelian systems relevant to the search for spin
liquids, and non-abelian systems relevant to topological quantum computation. I
will focus in particular on problems not reducible to free-fermion ones;
examples include the RVB state of electrons as well as models of quantum loops
and nets.
Amorphous materials (glasses) probably
constitute >90% of the solid matter surrounding us in everyday life,yet
traditional textbooks of condensed matter physics devote virtually no space to
them.Crudely speaking,the puzzles in the behavior of glasses can be divided
into three major areas:the glass transition itself,the characteristic long-term
memory effects and the near-equilibrium thermal,dielectric and transport
properties;this talk focusses entirely on the third area.Over the last 40 years
A simple physical realization of an integer quantum Hall
state of interacting two dimensional bosons is provided. This is an example of
a "symmetry-protected topological" (SPT) phase which is a
generalization of the concept of topological insulators to systems of
interacting bosons or fermions. Universal physical properties of the boson
integer quantum Hall state are described and shown to correspond to those
expected from general classifications of SPT phases.
I will briefly review topological phases of non
interacting fermions, such as topological insulators, and discuss how ideas
from quantum information, in particular the entanglement spectrum, can be used
to characterize them.
It has long been known that a metal near an instability
to antiferromagnetism also has a weak-coupling Cooper instability to
spin-singlet d-wave-like superconductivity.
However, the theory of the antiferromagnetic quantum
critical point flows to strong-coupling in two spatial dimensions, and so the
fate of the superconductivity has also been unclear.
We discuss the thermodynamic properties of the model
exchange quantum spin ice material Yb_2Ti_2O_7. Using exchange parameters
recently determined from high-field neutron scattering measurements, we
calculate the thermodynamic properties of this model system. We find very good
agreement with the heat capacity, entropy and magnetization measurements on the
materials. We show that, in the weak quantum regime, quantum fluctuations lead
to the selection, within the spin-ice manifold, of a conventional ordered
This talk will be about non-equilibrium many-body physics in integer quantum Hall edge states far from equilibrium. Recent experiments have generated a highly non-thermal electron distribution by bringing together at a point contact two quantum Hall edge states originating from sources at different potentials. The relaxation of this distribution to a stationary form is observed as a function of distance downstream from the contact [Phys. Rev. Lett. 105, 056803 (2010)]. I will discuss the broader context for the experiments and a physical picture of the equilibration process.
Electrons in conjugated organic polymers and molecules are strongly correlated since most of these systems are quasi one-dimensional. Experimental evidences include existence of two photons below one photon state, observation of negative spin densities in polyene radicals and qualitatively different behavior of optical gaps in polyenes and closely related symmetric cynanine dyes in the thermodynamic limiy. In this talk, I will introduce the model Hamiltonians for the electron states in conjugated systems.