The Vishwanath Group - UC Berkeley, Physics.

We are a Theoretical Physics group at UC Berkeley specializing in the study of Condensed Matter Physics. 
We seek to understand  properties of matter such as superconductivity and magnetism  starting from fundamental physical laws like quantum mechanics.  Historically, this has led to a deeper understanding of interacting quantum systems of very many particles as well as applications like the transistor, magnetic memories and magnetic resonance imaging . 

This wordle  gives you a picture of our current interests which includes  topological phases with strong interactions, unconventional quantum critical points and and three dimensional zero-gap semiconductors (i.e. Weyl and Dirac semimetals). We explore both the fundamental theory of such states, as well as their experimental signatures. 

We use a variety of theoretical tools, e.g. quantum field theory, but our research is primarily guided by interesting physical problems and ideas rather than techniques. We are happy to pick up new tools if they suite the problem at hand - for example we recently exploited concepts from quantum information theory to sharpen our understanding of topological phases.  We also work closely with experimental groups that  study interesting states of matter in solids and ultracold atomic systems. 

Recent Research Highlights:

  • Measuring space-group symmetry fractionalization in Z2 spin liquids (with Mike Zaletel and Yuan Ming Lu) arXiv:1501.01395
 We identify physical observables that distinguish different SETs in the context of Zquantum spin liquids with SU(2) spin rotation invariance. In the cylinder geometry we show that ground state quantum numbers for different topological sectors are robust invariants which can be used to identify the SET phase. More generally these invariants are related to 1D symmetry protected topological phases when viewing the cylinder geometry as a 1D spin chain. In particular we show that the Kagome spin liquid SET can be determined by measurements on one ground state, by wrapping the Kagome in a few different ways on the cylinder
  • Unified theory of spiral magnetism in the 3D harmonic honeycomb iridates  Li2IrO3: arxiv:14083640 (With Itamar Kimchi, Radu Coldea, James Analytis) We show that the Kitaev interaction stabilizes the counter-rotating spiral. By studying a minimal model of zig zag chains. This is argued to be the key to understanding of the remarkably similar magnetic ordering found in  two different structures of Li2IrO3.

Recent Group News:

  • Former postdoctoral fellows associated with the group, Sid Parameswaran, Xie Chen and Yuan Ming Lu move to faculty positions  at UC Irvine, Caltech and Ohio State respectively. Here is an interview with Xie Chen on joining Caltech.