Quantum Ice : a quantum Monte Carlo study

TL;DR

This paper uses quantum Monte Carlo simulations to demonstrate how quantum tunnelling lifts degeneracy in ice states, stabilizing a quantum liquid ground state with excitations akin to quantum electrodynamics, and discusses experimental distinctions.

Contribution

It introduces a computational study showing quantum tunnelling effects in ice states, leading to a novel quantum liquid ground state and identifying experimental signatures.

Findings

Quantum tunnelling lifts degeneracy in ice states.

Stabilization of a quantum liquid ground state with Maxwell-like excitations.

Distinguishing quantum ice from ordered states via neutron scattering.

Abstract

Ice states, in which frustrated interactions lead to a macroscopic ground-state degeneracy, occur in water ice, in problems of frustrated charge order on the pyrochlore lattice, and in the family of rare-earth magnets collectively known as spin ice. Of particular interest at the moment are "quantum spin ice" materials, where large quantum fluctuations may permit tunnelling between a macroscopic number of different classical ground states. Here we use zero-temperature quantum Monte Carlo simulations to show how such tunnelling can lift the degeneracy of a spin or charge ice, stabilising a unique "quantum ice" ground state --- a quantum liquid with excitations described by the Maxwell action of 3+1-dimensional quantum electrodynamics. We further identify a competing ordered "squiggle" state, and show how both squiggle and quantum ice states might be distinguished in neutron scattering experiments on a spin ice material.