# 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.

## Research plan of Yin-Chen He

Tuesday Mar 07, 2017
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In this talk, I will talk about my current study and the future directions that I am interested to explore, which include: (1) topological phases in cold atom, (2) spin liquid phases in frustrated magnets, (3) strongly interacting conformal field theory, (4) no equilibrium dynamics.  Specifically, I will elaborate on several topics that I plan to work on in the near future: (1) cold atom realization and detection of symmetry protected topological phases,

(2) effect of charge fluctuation in the spin liquid phases, (3) entanglement properties of 3D CFT.

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## Many-body localization: a quantum frontier

Monday Feb 27, 2017
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A closed quantum system is ergodic and satisfies equilibrium statistical physics when it completely loses local information of its initial condition under time evolution, by 'hiding' the information in non-local properties like entanglement. In the last decade, a flurry of theoretical work has shown that ergodicity can be broken in an isolated, quantum many-body system even at high energies in the presence of disorder, a phenomena known as many-body localization (MBL).

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## Boundary Hamiltonian theory for gapped topological phases on an open surface

Tuesday Feb 21, 2017
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In this talk we propose a Hamiltonian approach to 2+1D gapped topological phases on an open surface with boundary. The bulk part is

(Levin-Wen) string-net models arising from a unitary fusion category (can be viewed as Hamiltonian approach to extended Turaev-Viro TQFT), while the boundary Hamiltonian is constructed using any Frobenius algebra in the input category. The combined Hamiltonian is exactly solvable and gives rise to a gapped energy spectrum which is topologically protected.

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## Superconductivity near a quantum-critical point --- the special role of the first Matsubara frequency

Tuesday Feb 14, 2017
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Near a quantum-critical point in a metal strong fermion-fermion interaction mediated by a soft collective boson gives rise to incoherent, non-Fermi liquid behavior. It also often gives rise to superconductivity which masks the non-Fermi liquid behavior. We analyze the interplay between the tendency to pairing and fermionic incoherence for a set of quantum-critical models with effective dynamical interaction between low-energy fermions.

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## Generating RVB states in cavity-QED experiments

Tuesday Feb 07, 2017
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Dicke's seminal 1954 paper introduced the notion of `superradiance' in a system of spins coupled to a common photon mode.

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## Emergent Chiral Spin Liquids in Frustrated Magnetism

Friday Jan 20, 2017
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Topological states of matter are of of fundamental interest in contemporate condensed matter physics. Today, the fractional Quantum Hall effect remains the only known experimental system expected to exhibit intrinsic topological order. The question remains whether also different systems might stabilize this kind of ordering. Chiral spin liquids are an analogue of Fractional Quantum Hall Effect wave functions for spin systems. These wavefunctions have been envisioned in 1987 but only very recently several simple frustrated quantum spin models have been proposed realizing this physics.

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## Orders and disorder in high-Tc superconductors

Friday Jan 13, 2017
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Since its first discovery in 1986, high-Tc superconductors have been attracting constant interests and meticulous efforts from both theorists and experimentalists, not merely due to its large transition temperature, but also because it offers a well characterized laboratory for the study of exotic phenomena such as quantum criticality, non-Fermi liquid behavior, and intertwined orders. One pressing question in the field is the role played by disorder:

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## RG flows and Boundary States in 2d CFTs

Tuesday Jan 10, 2017
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## From skein theory to presentations of Thompson groups

Tuesday Jan 10, 2017
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Motivated by the question about reconstructing a Conformal field theory from the data of a subfactor of finite index, Jones studied the continuous limit of the periodic quantum spin chain which Thompson group acts on. Based on planar algebras, the topological axiomatization of subfactors, we will illustrate the idea of the correspondence between the skein theory of planar algebras and presentation of Thompson groups.

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## Theory and Experimental Platform for Bosonic Symmetry Protected Topological Phases

Tuesday Dec 20, 2016
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Bosonic symmetric protected topological (BSPT) phases are bosonic anagolue of electron topological insulators and superconductors. Despite the theoretical progresses of classifying these states, little attention has been paid to experimental realization of BSPT states in dimensions higher than 1. We propose bilayer graphene system in a out-of-plane magnetic field with Coulomb interaction is a natural platform for BSPT states with $U(1)\times U(1)$ symmetry.

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## LECTURES ON-DEMAND

### Roger Melko: Perimeter Institute and University of Waterloo

Speaker: Roger Melko