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날짜 2024-04-11 16:00 
일시 Apr 11(Thu), 16:00 
장소 E6-2, Rm#1323 
연사 Nanse Esaki (University of Tokyo) 
Nanse Esaki (Ph.D. student in Physics, The University of Tokyo)를 모시고 'Theoretical Studies of the Electric Field Induced Thermal Hall Effect in the Quantum Dimer Magnets XCuCl3 (X = Tl, K)' 주제에 대한 세미나를 개최하고자 합니다. 
물리학과 구성원 여러분들의 많은 참여 부탁드립니다.
 
1) Time : at 16:00 on Apr 11, 2024
2) Venue : E6-2, Rm#1323
3) Speaker : Nanse Esaki (Ph.D. student in Physics, The University of Tokyo)
4) Talk Title : Theoretical Studies of the Electric Field Induced Thermal Hall Effect in the Quantum Dimer Magnets XCuCl3 (X = Tl, K)
5) Abstract
   The thermal Hall effect in magnets has attracted increasing attention in recent years since it is a powerful probe of elementary excitations in solids and their nontrivial band topology. In quantum dimer magnets, where neighboring two = 1/2 spins form a dimer by the strong antiferromagnetic interaction, their elementary excitations are bosonic quasiparticle triplons. However, the thermal Hall effect of triplons has yet to be detected [1] although its candidate material has been proposed theoretically [2]. For this reason, we should seek other candidate materials exhibiting the thermal Hall effect of triplons.

 In this talk, I will present the theory of the electric field induced thermal Hall effect of triplons in the quantum dimer magnets XCuCl3 (X = Tl, K), which exhibit ferroelectricity in the Bose-Einstein condensation phase of triplons [3]. The interplay between ferroelectricity and magnetism in these materials leads to the magnetoelectric effect, i.e., an electric field induced Dzyaloshinskii-Moriya (DM) interaction between spins on the same dimer. In the high magnetic field regimes of the BEC phase where the lowest two modes are most relevant, we first consider the low-energy effective model [4] and find that there exist nodal lines in the Brillouin zone in the presence of an effective PT symmetry. Due to the presence of this symmetry, the system does not show the thermal Hall effect. However, the electric field induced intra-dimer DM interaction breaks the symmetry and gives rise to the thermal Hall effect. We also show that the magnitude (the direction) of the thermal Hall current can be well controlled by changing the strength (the direction) of the electric field.

 Additionally, we investigate the thermal Hall effect in lower magnetic field regimes of the BEC phase, considering all triplon modes. We identify that nodal lines protected by symmetries still exist without an electric field, although the effective PT symmetry does not. Interestingly, the thermal Hall effect in the lower magnetic field regimes can also be well controlled by an electric field, similar to the effective model for high magnetic field regimes.

 We anticipate that the thermal Hall effect in XCuCl3 can be detected in experiments with achievable electric and magnetic fields. Moreover, in the lower magnetic field regimes, we discover that an electric field can induce Weyl triplons, leading to multiple topological phase transitions by tuning a magnetic field with a finite electric field.

 

References
[1] S. Suetsugu et al., Phys. Rev. B 105, 024415 (2022).

[2] J. Romhányi, K. Penc, and R. Ganesh, Nat. Commun. 6, 6805 (2015).

[3] S. Kimura et al., Nat. Commun. 7, 12822 (2016).

[4] N. Esaki, Y. Akagi, and H. Katsura, arXiv: 2309.12812.

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