[Seminar] Localisation phenomena in frustrated magnets
Prof. Claudio Castelnovo
University of Cambridge, Cavendish Laboratory, Theory of Condensed Matter group
Prof Claudio Castelnovo has published on the thermodynamics and equilibration properties of frustrated magnetic systems, classical and quantum spin liquids, slow dynamics in non-disordered systems, and out of equilibrium properties in systems with fractionalised excitations. Following an EPSRC Postdoctoral Fellowship (2009-2012) at the University of Oxford, he became a lecturer at Royal Holloway in 2010 and moved to Cambridge in 2012. He was co-recipient of the EPS Europhysics Prize (2012) and received the IUPAP C10 Young Scientist Prize (2013). He is a co-organiser of CMP in the City, TEMM, and the Advanced Working Group series, and has been a lecturer at a Les Houches Summer School (2019) and at an ICTP-MPIPKS Winter School (2020). He co-organised the ICTP Summer School on Collective Behaviour in Quantum Matter (2018 and 2022).
Localisation phenomena in frustrated magnets
Elementary excitations in frustrated magnetic systems often take the form of fractionalised point-like quasiparticles. In recent years significant progress was made to understand the nature of these excitations and the importance of their effective description to gain insight into the thermodynamic properties of frustrated systems. Their dynamics on the other hand remains to date a significantly taller order. Whereas in a few cases the quasiparticles can be modelled as free, their interplay with the underlying spin vacuum of which they are borne is generally highly nontrivial. The result is a rich playground of constrained motion, reduced (fractal) dimensionality, and self-generated disorder, giving rise to intriguing instances of slow dynamics and localisation which may be accessible in state of the art experiments on magnetic systems. This talk reviews some key examples, in the context of U(1) spin ice and Z_2 spin liquids, and a compass model of complex oxides. In the U(1) case, dynamical constraints lead to quasi-1D motion on random comb structures where configurational disorder produces compact localised states that survive in presence of interactions. In the Z_2 case, correlation holes induced by semionic statistics give rise to long-lived metastable states and strong out-of-equilibrium behaviour. Finally, in the compass model, disorder free localisation results in dynamical behaviour characteristic of many-body-localised system, including the logarithmic growth of entanglement; this is all the more exciting since signatures are accessible in certain components of the dynamical structure factor, experimentally measurable in the magnetic oxides described by this model.
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