Mott-insulator to commensurate-solid transition in a 4He layer on \alpha-graphyne: Pseudo-spin symmetry breaking under a particle-induced pseudo-magnetic field

TL;DR

This study uses path-integral Monte Carlo to explore how $^4$He atoms adsorbed on $ ext{α}$-graphyne undergo a transition from a Mott insulator to a commensurate solid, revealing pseudo-spin symmetry breaking akin to magnetic phenomena.

Contribution

It demonstrates the particle-induced pseudo-magnetic field effect causing a transition from a spin liquid to a ferromagnet in helium layers on $ ext{α}$-graphyne, a novel insight into quantum phase transitions.

Findings

Identification of a Mott insulating state at specific helium density.

Observation of a transition to a commensurate triangular solid.

Pseudo-spin symmetry breaking induced by additional helium atoms.

Abstract

Path-integral Monte Carlo calculations were performed to study the adsorption of $^4$He atoms on $\alpha$-graphyne. We find that one $^4$He atom can be embedded onto the in-plane center of each hexagon of the graphyne. In the first $^4$He layer above the $^4$He-embedded graphyne surface, a Mott insulating state was observed at the areal density of 0.0706 \AA$^{-2}$ with three $^4$He atoms occupying each hexagonal cell while the helium atoms form a commensurate triangular solid at a density of 0.0941 \AA$^{-2}$. Here we show that the Ising pseudo-spin symmetry introduced for two degenerate configurations of three $^4$He atoms in a hexagonal cell can be broken by additional $^4$He atoms placed at the hexagon vertices and the Mott-insulator to commensurate-solid transition is a transition from a nonmagnetic spin liquid of frustrated antiferromagnets to a spin-aligned ferromagnet under a particle-induced pseudo-magnetic field.