UMR 5672

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Coulomb and Harmonic Phases in Spin Ice and Polar Liquids

Steven Bramwell (University College London)
When Jan 22, 2018
from 11:00 AM to 12:00 PM
Where Amphi. Schrödinger
Attendees Steven Bramwell
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Many liquid or liquid-like states remain stable down to temperatures well below the interaction energy scale, where mean-field theory predicts an ordering transition. In magnetism, correlated states such as spin ice and the spin liquid have been described as Coulomb phases, governed by an emergent gauge principle. In the physical chemistry of polar liquids, systems that evade mean field order have, in contrast, been described by Onsager’s theory of the reaction field. In this talk I will describe how, in the low-temperature limit, Onsager’s theory may be cast as a prototypical theory of the Coulomb phase. However at finite temperature, it describes a distinct geometrical state, characterised by harmonic functions. This state, which I call the "harmonic phase", is shown to occur experimentally in spin ice, a dipolar lattice system, already famous for its emergent magnetic "monopoles".
 

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