# Joint PITT-CMU Colloquium: Joel Moore (UC Berkeley)

### January 30, 2017 - 9:30pm to 11:00pm

Title: New topological phases and effects in solids

Abstract: Much of condensed matter physics is concerned with understanding how

different kinds of order emerge from interactions between a large number

of simple constituents. In ordered phases such as crystals, magnets, and

superfluids, the order is understood through "symmetry breaking": in a

crystal, for example, the continuous symmetries of space under rotations and

translations are not reflected in the ground state. A major discovery of the 1980s

was that electrons confined to two dimensions and in a strong magnetic field

exhibit a completely different, topological type of order that underlies

the quantum Hall effect.

Topological order also occurs in some materials, dubbed "topological insulators”,

in zero magnetic field. Spin-orbit coupling, an intrinsic property of all solids, drives

the formation of the topological state. There are also topological Dirac and Weyl

semimetals that generalize the massless electronic structure of graphene to 3D.

This talk will explain what topological order means, then give an overview of

the new topological phases and the unusual transport and optical responses they

enable.

### Location and Address

102 Thaw Hall