Experimentally tunable QED in dipolar-octupolar quantum spin ice

TL;DR

This paper proposes an experimental method to tune emergent quantum electrodynamics in dipolar-octupolar quantum spin ice using magnetic fields, enabling control over photon speeds and inducing novel phase transitions.

Contribution

It introduces a practical approach to manipulate eQED properties in quantum spin ice, including controlling photon velocities and inducing phase transitions, which has not been demonstrated before.

Findings

Magnetic field can tune the emergent speed of light in quantum spin ice.

Different field alignments can produce distinct photon polarization speeds, akin to the electro-optic Kerr effect.

Predicted field-induced phase transitions, including between flux phases and frustrated flux configurations.

Abstract

We propose a readily achievable experimental setting where an external magnetic field is used to tune the emergent quantum electrodynamics (eQED) of dipolar-octupolar quantum spin ice (DO-QSI). In $U(1)_\pi$ DO-QSI -- the proposed ground state of QSI candidates Ce$_2$Zr$_2$O$_7$, Ce$_2$Sn$_2$O$_7$ and Ce$_2$Hf$_2$O$_7$ -- we show that the field can be used to control the emergent speed of light (and, consequently, the emergent fine structure constant). Depending on the field's alignment with the crystal, one may induce different speeds for the two polarizations of the emergent photons, in a fascinating analogue of the electro-optic Kerr effect. In $U(1)_0$ DO-QSI -- yet to be uncovered experimentally -- we find a number of unusual field-induced transitions, including a transition between $0$- and $\pi$-flux QSI phases, as well as phases with frustrated flux configurations. We discuss experimental signatures of these effects in the spinon excitation spectrum, which can be readily accessed for instance in inelastic neutron scattering measurements. Our proposal opens the gate to a plethora of experimentally accessible, engineerable eQED phenomena in the emergent universes of quantum spin ice.