# Condensed Matter Seminar Series

## Exotic Quantum Critical Points

### Matt Hastings

#### Duke University

##### Thursday September 8, 4:00pm, Room 299, Physics Building

(note irregular time and place)

Abstract:
The standard paradigm for describing critical phenomena is the Landau
paradigm of symmetry breaking, but it was proposed in the last decade
that so-called "exotic" or "de-confined" quantum critical points may
exist that lie outside this paradigm. However, despite extensive
theoretical work, the existence of such critical points in concrete
lattice Hamiltonians remained controversial: possible candidates exist
but the interpretation of the numerical data is in question. I'll talk
about recent work with Roger Melko and Sergei Isakov presenting strong
evidence for the existence of such a critical point, the so-called XY*
point involving condensation of fractionalized particles carrying
conserved U(1) charge coupled to a Z_2 gauge theory. By a
combination of studying scaling of familiar quantities like the
correlation function (where we find a strongly nonclassical exponent)
with studying scaling of novel functions of the winding number
distribution (which directly probe topological properties of the
discrete gauge theory), we present "smoking gun" evidence for such a
point in a Bose-Hubbard model.

*Host: Harold Baranger*