Research: Topological Route to New and Unusual Coulomb Spin Liquids

Classical spin liquids arise when a magnet has many degenerate ground states, defined by a local constraint. Coulomb spin liquids are a type of classical spin liquid where the local constraint can be mapped to a Gauss’s law, like that which appears in the theory of electromagnetism. Recently, ‘higher rank’ Coulomb spin liquids have been pointed out, in which the local constraint looks like a Gauss’s law for a rank-2 tensor electric fields. These higher rank spin liquids are of great interest because of a connection with fractons: particles that can never move when isolated. 

A few models are known which realise Coulomb spin liquids, both of ordinary and higher-rank types, but a systematic understanding which encompasses all the different kinds has been lacking. This systematic understanding has been found in new research within project A01 of SFB 1143. The researchers showed how Coulomb spin liquids are characterised by topological defects in momentum space, which show up in the spin correlation functions. This enabled the construction of models where a series of distinct Coulomb spin liquids are realized, with phase transitions between them. Higher rank Coulomb liquids appear at the phase boundaries between ordinary Coulomb liquids. This work opens a door to a more general classification of classical spin liquids, based on a topological characterisation.

O. Benton, R. Moessner,
Topological Route to New and Unusual Coulomb Spin Liquids,
Phys. Rev. Lett. 127, 107202 (2021) (arXiv)