Superfluid transition of the second layer of He-4 on graphite: does substrate corrugation matter?

TL;DR

This study uses Quantum Monte Carlo simulations to investigate how substrate corrugation influences the superfluid transition of the second He-4 layer on graphite, finding a modest reduction in superfluidity but no evidence of supersolid phases.

Contribution

It provides a detailed microscopic analysis of substrate corrugation effects on superfluidity in He-4 layers, contrasting with smooth substrate models.

Findings

Corrugation reduces superfluid fraction by ~20%.

No evidence of commensurate crystalline or supersolid phases.

Superfluid transition temperature estimated at ~0.75 K.

Abstract

The second layer of He-4 adsorbed on a graphite substrate is studied by Quantum Monte Carlo simulations. We make use of a microscopic model of the substrate fully accounting for its corrugation, and compare the results to those obtained with a smooth substrate. The only effect of corrugation is a ~20% reduction of the value of the superfluid fraction of the top layer, in the limit of zero temperature. No evidence of any commensurate (7/12) crystalline and/or "supersolid" phase is found; the superfluid transition temperature is estimated to be ~ 0.75 K. We discuss the implication of these findings on the interpretation of recent experiments.