Hard core repulsion and supersolid cluster crystals

TL;DR

This study investigates how a short-range hard-core repulsion influences the stability and superfluidity of 2D soft core boson cluster crystals, revealing that a very short-range repulsion does not alter phase properties, but larger ranges can induce a transition to a superfluid.

Contribution

It demonstrates that the physical properties of 2D soft core boson cluster crystals are robust against strong, very short-range hard-core repulsions, and identifies the critical range for phase transition.

Findings

Short-range hard-core repulsion does not alter phase properties if the range is very small.

A hard core with a range over 5% of cluster size can destabilize the crystal into a superfluid.

Moderate inner core repulsion enhances the superfluid response.

Abstract

We study the effect of a short-ranged hard-core repulsion on the stability and superfluid properties of the cluster crystal phase of two-dimensional (2D) soft core bosons. Results of Quantum Monte Carlo simulations on a cogent test case suggest that the main physical properties of the phase remain unaltered if the range d of the inner repulsive core is sufficiently short, even if the strength of the repulsion is several orders of magnitude greater than the outer soft core barrier. Only if d is an appreciable fraction of the size of the clusters (> 5%) does a sufficiently strong hard core repulsion cause the crystal to break down into a homogeneous superfluid; a moderate inner core repulsion enhances the superfluid response of the crystalline phase.