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Speaker: Piers Coleman (Center for Materials Theory, Rutgers University)

Over the past two decades, research into quantum materials has reverberated under the impact of new concepts, particularly, those of topology and fractionalization. This talk will bring these two ideas together with the idea of broken symmetry. When a spin fractionalizes into a fermion, the resulting particle can hybridize or pair with the mobile electrons to develop a new kind of fractional order parameter. The concept of "order fractionlization" enables us to extend the concept of off-diagonal order to encompass the formation of such order parameters with fractional quantum numbers, such as spinorial order[1].

A beautiful illustration of this phenomenon is provided by a model which incorporates a solvable gapless spin liquid - the "Yao-Lee-Kitaev model" into a Kondo lattice[2]. This model explicitly exhibits order fractionalization, and is expected to undergo a discrete Ising phase transition at finite temperature into an order-fractionalized phase with gapless Majoranas. The broader implications of these considerations for Quantum Materials and Quantum Field Theory will be discussed.

* Work done in collaboration with Yashar Komijani, Anna Toth, Premi Chandra and Alexei Tsvelik.

[1] Order Fractionalization, Yashar Komijani, Anna Toth, Premala Chandra, Piers Coleman, (2018).
[2] Order Fractionalization in a Kitaev Kondo model, Alexei Tsvelik, Piers Coleman, (2021).

Host:  Sang-Wook Cheong