Condensed Matter Seminar

Anders W. Sandvik
Boston University

Thursday, September 24, 2009
1:00 pm in SPL 52

Evidence for deconfined quantum-criticality in a class of extended Heisenberg models

Abstract: I will discuss the quantum phase transition between an antiferromagnetic (AF) and valence-bond-solid (VBS) ground state of interacting quantum spins in two dimensions. It has been proposed [Senthil et al., Science 303, 1490 (2004)] that this transition is associated with spinon deconfinement and an emergent U(1) symmetry when the critical point is approached from the VBS side. This scenario has remained controversial. I will here discuss quantum Monte Carlo results for a class of Heisenberg models including multi-spin interactions, which can be tuned between AF and VBS phases. These results support a universal quantum-critical point, with an emergent U(1) symmetry which is governed by a divergent length scale different from the correlation length. This length should correspond to the size of a spinon pair.