This series consists of talks in the area of Condensed Matter.
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.
Large quantum fluctuations in certain quantum spin systems destroy long range magnetic order such as antiferromagnetism. Resulting paramagnetic states are called a quantum spin liquids. These states support emergent gauge fields [1]. Under certain conditions, emergent gauge fields condense in the ground state, leading to a chiral spin liquid state [2]. A condensed `magnetic field' for example, correspond to presence of spontaneous circulating spin current or spin `chirality'[3].
The ground state phase of spin-1/2 J1-J2 antiferromagnetic Heisenberg model on square lattice in the maximally frustrated regime (J2 ~ 0.5J1) has been debated for decades. Here we study this model by using a recently proposed novel numerical method - the cluster update algorithm for tensor product states (TPSs). The ground state energies at finite sizes and in the thermodynamic limit (with finite size scaling) are in good agreement with the state of art exact diagonalization study, and