CPM Seminar

Universal Scaling in the Fan of Deconfined Quantum Criticality

Roger Melco

Department of Physics
University of Waterloo

The modern theory of quantum phase transitions hinges upon the idea of an observable order parameter, related to broken symmetries of the ordered phases, whose fluctuations govern universal properties at criticality. This paradigm has recently been challenged by Senthil and coworkers, who proposed the existence of a “deconfined” quantum critical point (DQCP) - a generic continuous quantum phase transition separating phases with unrelated broken symmetries, and with exotic emergent properties. We present the results of quantum Monte Carlo simulations on a 2D S=1/2 Heisenberg model with additional four-spin interaction, which appears to be the first microscopic model potentially harboring a DQCP. Using extensive simulations on lattice sizes containing in excess of 10⁴ spins, we examine the candidate Néel to valence-bond-solid (VBS) quantum phase transition, focussing on finite-temperature properties of the quantum critical fan, including scaling behavior, the calculation of universal critical exponents, and the apparent emergence of a global topological degeneracy in the VBS order parameter.