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.