Frustration from Frustration: Field Tuning, Vison Crystallisation, and Disorder in Quantum Spin Ice

Quantum spin ice (QSI) is one of the oldest and most widely known models of a U(1) quantum spin liquid – a fascinating phase of matter in which quantum electrodynamics emerges at low energies in a frustrated magnet. This playground for alternate-universe electromagnetism exhibits many phenomena beyond standard theory, including strong- coupling confinement, Dirac monopoles, axions and theta terms. Excitingly, recent experiments on the Ce based pyrochlore Ce Zr O have produced compelling evidence in support of a QSI ground state – after 20 years confined to the notebooks of theorists, it would now appear that the community is close to a quantum spin ice discovery. In the first part of this thesis, I introduce a model of ‘breathing’ quantum spin ice captured at low energy by a new kind of staggered gauge theory. This theory shows a strongly first order transition to an inversion-broken phase, which may be thought of as a zinc blende packing of Dirac monopoles (visons) in the emergent gauge theory. This theory’s phase diagram exhibits ‘flux frustration’, a peculiar phenomenon in which not just the magnetic moments, but also the fluxes of the emergent gauge field become frustrated. I then outline a more realistic setting giving rise to flux frustration, demonstrating that a [111] field applied to a dominantly octupolar quantum spin ice (such as the interesting candidate Ce Hf O ) drives a quantum phase transition into a state which we tentatively call a ‘flux liquid’. Further, I show that the applied magnetic field coherently modulates the emergent QED, giving rise to anisotropic electromagnetism with practically observable spectroscopic and thermodynamic signatures. Finally, I consider the question of site disorder in quantum spin ice, exhibiting a mechanism by which a small number of non-magnetic impurities can nucleate strongly gapped singlets that effectively deactivate large regions of the system. This ‘diluted QSI’ model provides an upper bound on the allowable disorder levels that QSI can survive. Our model shows signs of a localised, gapped photon even at the modest 9% impurity concentration reported in experiments, underscoring the critical importance of ultra-clean samples to seeing spin-liquid physics in experiment.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Sanders, Alaric

Advisor dc:contributor.advisor

• Castelnovo, Claudio

• Gauge Theory
• Magnetism
• Quantum Spin Ice

Licence

• https://www.repository.cam.ac.uk/bitstreams/df1714ab-0bce-4e03-a708-2d157d60b388/download
• https://creativecommons.org/licenses/by-sa/4.0/

Language dc:language

eng

Author Identifier

0000-0003-4283-0566

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/397928