Claudio Castelnovo

University of Cambridge



Quantum spin liquids (QSLs) are an interesting and often enigmatic phase of matter that exhibits some of the most exciting phenomena uncovered in modern condensed matter physics over the last few decades, from emergent symmetries and topological order, to fractionalised excitations and fractional statistics. QSLs remained for a long time largely the remit of theoretical physics. However, in recent years more and more candidate materials are being proposed and investigated, with a shift in focus to characterise and diagnose them to definitively confirm their spin liquid behaviour. Correspondingly, a theoretical interest has arisen to understand their finite temperature behaviour, both as an experimental inevitability, but also as an effort to look for possible finite temperature precursor properties that may tell the tale of a QSL at lower, more difficult to access, temperatures. In this talk we explore this intermediate temperature regime in a class of QSLs that are characterised by a large (classical) projective energy scale and weaker quantum fluctuations — as is the case in model systems such as the six or eight vertex models in a transverse field, closely related respectively to quantum spin ice and the toric code. Whereas a general framework to understand the finite temperature behaviour of these systems remains a tall order, we illustrate the rich range of phenomena that one may expect — encompassing configurational localisation, compact localised states, and statistics-driven phase separation — in a few model systems. Furthermore, we discuss how these phenomena may be used to diagnose and understand QSL response and thermodynamic properties in real materials.

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