Separation of two regimes in a disordered boson Hubbard Model

TL;DR

This paper investigates the insulator-to-superfluid transition in a disordered 2D boson Hubbard model at zero temperature, revealing a multi-critical point with a dynamical critical exponent of approximately 1.5, and highlighting the role of density fluctuations in the transition.

Contribution

It provides the first Monte Carlo analysis of the critical behavior in the disordered boson Hubbard model, identifying a multi-critical point and the influence of density fluctuations on the transition.

Findings

Dynamical critical exponent z=1.5 ± 0.1 supports multi-critical behavior.

Density fluctuations from particle-hole excitations drive the transition in weak disorder.

Evidence of two regimes separated by a multi-critical point.

Abstract

We study the insulator-to-superfluid transition in a two-dimensional disordered boson Hubbard model at zero temperature for intermediate strength of disorder at commensurate density. Via Monte Carlo calculations of the correlation functions in the integer current representation of the model, we obtain the dynamical critical exponent $z=1.5 \pm 0.1$, supporting the multi-critical behavior separating the strong and weak disorder regimes. Investigating the density profile, we suggest that the density fluctuations due to the particle-hole excitations drive the transition in the weak disorder regime.