Date/Time
Date(s) - 18/11/2015
3:30 pm - 4:30 pm

Title: Anomalous Scaling in Critical Quantum Magnets

Speaker: Dr. Anders W. Sandvik

Institute: Boston University

Location: ABB 102

Description:

Finite-size scaling is a well-established method for analyzing Monte Carlo simulation data close to critical points. Singular quantities scale as a power of the system size (length) L times a function of the ratio of the intrinsic correlation length and L. There is a generalization to cases where there are two divergent length scales, which has been theoretically
predicted at certain “deconfined” transitions in two-dimensional quantum magnets. Quantum Monte Carlo simulation data for candidate models realizing such transitions have been difficult to interpret, however. In this talk I will first review the method of finite-size scaling in a simple classical
setting, before moving on to conventional quantum phase transitions with a single divergent length scale (correlation length). I will then discuss a model which realizes a deconfined phase transition between an anti-ferromagnet
and a non-magnetic dimerized state. Here one can observe that the size of a bound (confined) state of two excited spinons diverges faster than the spin correlation length, and a modified scaling hypothesis involving two divergent lengths can explain all calculated physical observables. The study
points to an unexpected richness of deconfined quantum-criticality, including violations of experimentally important finite-temperature scaling laws.