סמינר בחומר מעובה: Spin jam, tessellations and exotic entropy in frustrated magnets

Abstract:

When spins are regularly arranged in a triangular fashion, the spins may not satisfy simultaneously their antiferromagnetic interactions with their neighbors. This phenomenon, called frustration, may lead to a large set of ground states and to exotic states such as spin ice and spin liquid. However, when frustration is present simultaneously with disorder, a spin-glass is known to be a typical state of such a magnetic system. Is disorder necessary for a spin glass to form? This fundamental question has been frequently asked and several theoretical models of clean glassy states has been proposed, typically relying on long range interactions. Motivated by puzzling behavior observed in a well studied magnetic systems (SCGO), I describe a novel mechanism wherein quantum fluctuations cause a clean system governed by simple local interactions to freeze into a glass. At the heart of the effect is an unusual scaling of the number of local minima, with a scaling extensive in the boundary length rather than the volume. I will explain how these properties follow by a combination of tools and mappings, leading to a problem of counting tessellations. I will also present recent experimental evidence for the spin jam scenario.

References:  [1] I Klich, SH Lee and K Iida, Nature com (2014);  [2] Yang et al. PNAS 112 (37), 11519-11523 (2015); [3] Samarkoon et al. 113 (42), 11806-11810 PNAS (2016)

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