Seeing the light : experimental signatures of emergent electromagnetism in a quantum spin ice

TL;DR

This paper investigates how quantum spin ice materials exhibit emergent electromagnetism, predicting experimental signatures such as the disappearance of pinch points and the appearance of photon-like excitations, supported by theoretical and simulation results.

Contribution

It develops a lattice field theory for quantum spin ice and predicts observable experimental signatures of emergent electromagnetism, advancing understanding of quantum spin liquids.

Findings

Pinch points fade at zero temperature in quantum spin ice.

Linearly dispersing magnetic excitations ('photons') are predicted.

Field theory predictions agree with Quantum Monte Carlo simulations.

Abstract

The "spin ice" state found in the rare earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 offers a beautiful realisation of classical magnetostatics, complete with magnetic monopole excitations. It has been suggested that in "quantum spin ice" materials, quantum-mechanical tunnelling between different ice configurations could convert the magnetostatics of spin ice into a quantum spin liquid which realises a fully dynamical, lattice-analogue of quantum electromagnetism. Here we explore how such a state might manifest itself in experiment, within the minimal microscopic model of a such a quantum spin ice. We develop a lattice field theory for this model, and use this to make explicit predictions for the dynamical structure factor which would be observed in neutron scattering experiments on a quantum spin ice. We find that "pinch points", seen in quasi-elastic scattering, which are the signal feature of a classical spin ice, fade away as a quantum ice is cooled to its zero-temperature ground state. We also make explicit predictions for the ghostly, linearly dispersing magnetic excitations which are the "photons" of this emergent electromagnetism. The predictions of this field theory are shown to be in quantitative agreement with Quantum Monte Carlo simulations at zero temperature.