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Magnetic properties in the generalized Kitaev model

Date : Friday, December 13th, 2019 16:00 〜 Place : Seminar Room 5 (A615), 6th Floor, ISSP Lecturer : Prof. Akihisa Koga Affiliation : Department of Physics, Tokyo Institute of Technology Committee Chair : Naoki Kawashima (63260)
e-mail: kawashima@issp.u-tokyo.ac.jp

The Kitaev model [1] have attracted much interest in condensed matter physics since the possibility of direction-dependent Ising interactions has been proposed in realistic materials [2]. One of the important features characteristic of the Kitaev models is the fractionalization of the spin degree of freedom. In the Kitaev model with S = 1/2 spins, the spins are exactly shown to be fractionalized into itinerant Majorana fermions and localized fluxes. Two energy scales for distinct degrees of freedom yield interesting finite temperature properties, such as a double-peak structure in the specific heat and plateau in the entropy [3]. This fractionalization is closely related to the existence of the local Z2 symmetry in the system.
The existence of the local Z2 symmetry is known even in the generalized spin-S Kitaev model [4], while it is still unclear whether or not the spin fractionalization occurs in the system. To clarify this, in this study, we examine thermodynamic properties in the generalized Kitaev model by means of the thermal pure quantum state method. We then clarify the existence of the double-peak structure in the specific heat and plateau in the entropy [5]. These suggest the existence of fractionalization even in this spin-S Kitaev model. Magnetic properties in the mixed-spin Kitaev model are also discussed.

[1] A. Kitaev, Ann. Phys. 321, 2 (2006).
[2] G. Jackeli and G. Khaliullin, Phys. Rev. Lett. 102, 017205 (2009).
[3] J. Nasu, M. Udagawa, and Y. Motome, Phys. Rev. B 92, 115122 (2015).
[4] G. Baskaran, D. Sen, and R. Shankar, Phys. Rev. B 78, 115116 (2008).
[5] A. Koga, H. Tomishige, and J. Nasu, J. Phys. Soc. Jpn. 87, 063703 (2018).


(Published on: Wednesday November 27th, 2019)