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.

Topological entropies in the classical toric code model - An information theory perspective

Tuesday Nov 17, 2015
Speaker(s):

Concepts of information theory are increasingly used to characterize collective phenomena in condensed matter systems, such as the use of entanglement entropies to identify emergent topological order in interacting quantum many-body systems. Here we employ classical variants of these concepts, in particular Renyi entropies and their associated mutual information, to identify topological order in classical systems.

Collection/Series:
Scientific Areas:

Conserved momenta of a ferromagnetic soliton

Friday Nov 13, 2015
Speaker(s):

Solitons in a ferromagnet have interesting dynamics because atomic magnetic moments behave like little gyroscopes. A domain wall in a magnetic wire can be modeled as a bead on a string: it has two soft modes, position and orientation. This "bead" rotates when it is pushed and moves when twisted.

Collection/Series:
Scientific Areas:

Entanglement Entropy Scaling Laws and Eigenstate Thermalization in Many-Particle Systems

Tuesday Nov 10, 2015
Speaker(s):

While entanglement entropy of ground states usually follows the area law, violations do exist, and it is important to understand their origin. In 1D they are found to be associated with quantum criticality. Until recently the only established examples of such violation in higher dimensions are free fermion ground states with Fermi surfaces, where it is found that the area law is enhanced by a logarithmic factor. In Ref. [1], we use multi-dimensional bosonization to provide a simple derivation of this result, and show that the logarithimic factor has a 1D origin.

Collection/Series:
Scientific Areas:

Multitude of percolative orders: Infinite cascades of geometric phase transitions

Tuesday Nov 03, 2015
Speaker(s):

The evolution of many kinetic processes in 1+1 dimensions results in 2D directed percolative landscapes. The active phases of those models possess numerous hidden geometric orders characterized by distinct percolative patterns.

Collection/Series:
Scientific Areas:

Bose condensation in category theory

Tuesday Oct 27, 2015
Speaker(s):

The condensation of bosons can induce transitions between topological quantum field theories (TQFTs). This as been previously investigated through the formalism of Frobenius algebras and with the use of Vertex lifting coefficients. I will discuss an alternative, algebraic approach to boson condensation in TQFTs that is physically motivated and computationally efficient.

Collection/Series:
Scientific Areas:

Many-body localization and thermalization in disordered Hubbard chains

Monday Oct 26, 2015
Speaker(s):

In this talk, I will revise some of the aspects that lead isolated interacting quantum systems to thermalize.

In the presence of disorder, however, the thermalization process fails resulting in a phenomena where

transport is suppressed known as many-body localization. Unlike the standard Anderson localization for

non-interacting systems, the delocalized (ergodic) phase is very robust against disorder even for moderate

values of interaction. Another interesting aspect of the many-body localization phase is that under the time

Collection/Series:
Scientific Areas:

Descent Equations, Gauge Structure in Configuration Space and Topology of Quantum Field Theory - Yongshi Wu

Wednesday Oct 14, 2015
Speaker(s):

Topological aspects of physical systems, including the called topological states of matter, have become hot topics in the frontiers of physics in recent years. Here I would like to present a mathematically "popular" talk for professional physicists for a highlight or overview of how one can systematize knowledge of topological aspects of quantum field theories. Our starting points are Descent Equations and Gauge Structure in Configuration Space in Field Theory. (The audience needs only to know the meaning of "differential forms".)

Collection/Series:
Scientific Areas:

Orbital Angular Momentum and Spectral Flow in Two Dimensional Chiral Superfluids

Tuesday Sep 29, 2015
Speaker(s):

The orbital angular momentum in a chiral superfluid has posed a paradox for several decades. For example, for the $p+ip$-wave superfluid of $N$ fermions, the total orbital angular momentum should be $N/2$ if all the fermions form Cooper pairs. On the other hand, it appears to be substantially suppressed from $N/2$, considering that only the fermions near the Fermi surface would be affected by the pairing interaction.

Collection/Series:
Scientific Areas:

Matrix product operators and topological quantum order

Monday Aug 24, 2015
Speaker(s):

Matrix product operators form a natural language for describing topological quantum order. I will discuss how they arise as symmetries in PEPS, how anyon excitations arise as end points on them, and how the virtual indices of the MPO's provide a tensor product structure for the logical qubits in topological quantum computation.

Collection/Series:
Scientific Areas:

Using anomaly tests to restrict crystal symmetry fractionalization in Z_2 and chiral spin liquids

Tuesday Aug 11, 2015
Speaker(s):

Using the method of flux fusion anomaly test recently developed by M. Hermele and X. Chen (arXiv:1508.00573), we show that the possible ways of fractionalize crystal symmetry is greatly restricted if we assume the spin liquid has an SU(2) spin rotation symmetry and the spinon carries a half-integer spin. For a Z_2 spin liquid, under these assumptions the vison can only take the crystal symmetry fractionalization described by the Ising gauge theory.

Collection/Series:
Scientific Areas: