July 20, 2015 – July 22, 2015

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Location

Cambridge, United Kingdom

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Organizers

Claudio Castelnovo, UK NESFE
Roderich Moessner, MPIPKS
David Logan, University of Oxford

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Overview

http://www.tcm.phy.cam.ac.uk/awgif/ 

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Systems where itinerant electrons coexist with localised magnetic moments on frustrated lattices have been argued to exhibit remarkably rich phase diagrams and to host novel and interesting emergent behaviour. Examples of materials in this class include the pyrochlore Praseodymium Iridate or the spinel Lithium Vanadate. On the one hand, the conduction electrons alone present a wide range of behaviours, from Weyl semimetals to fractional Cern insulators. On the other hand, the situation becomes even richer when the frustrated localised moments form non-coplanar magnetisation patterns, giving rise for instance to anomalous Hall transport properties.

 

Understanding these systems requires efforts at the interface between itinerant electron physics, frustrated magnetism, Kondo lattices and periodic Anderson models, heavy fermions and Chern insulators. Strong spin orbit coupling is also likely to play a fundamental role. Moreover, the localised moments are usually multielectron states with anisotropic crystal field environments, whereby it is too simplistic to model the interaction with the itinerant electrons as the scalar product of two vector spin operators.

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With this workshop, we would like to bring together a small group of leading scientists in these areas, together with some promising junior researchers, to actively share and discuss the materials, phenomenology, and techniques. What we have in mind is a 2-day Advanced Working Group, with 4-5 invited overview talks that present not only the spearers own work but also a general view of the state of the art of the respective areas of research. Each overview talk will be followed by long organised discussion session as well as breakout sessions. Contributed talks by the other participants are optional and will be strictly selected (8-10 at the very most) and expected to be brief and to the point (10-15min). In addition to the overview speakers, the list of participants will include some of the leading senior scientists in related areas of research as well as postdocs / young researchers who have done some work or demonstrated serious interest in these areas. We aim for a 50-50 ratio of senior and junior participants. The event is designed for a sufficiently small group of selected participants (approx. 25-30) where we can be reasonably confident that the desired level of scientific discussion and exchange is achieved. For this reason, we would like to make the event by invitation only.

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Some of the questions that we aim to address during the workshop are:

 

How does the coupling between itinerant and localised moments take place at a microscopic level? How can we model it most effectively? We expect that a compromise must be made between the overly-simplified spin vector scalar product and, say, a full crystal field Hamiltonian.

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Given a choice of microscopic (effective) interaction, how do we study the collective behaviour of these systems? One might need to study a local d-manifold and a f-manifold to obtain an effectiveHamiltonian, before venturing into studying the collective behaviour. How do we compare and what can we learn from different theoretical approaches, for example approximating the frustrated moments as static background (time scale separation), bosonisation techniques applied to topological Kondo insulators, mean field vs. Gauge mean field theory?