首頁/演講活動/回上頁
109學年度 下學期 碩博班專題討論(Colloquium)

Quantum spin liquids on 2D geometrically frustrated lattice

演講者 : 高英哲 教授 (國立臺灣大學物理系)
演講時間 : 2021 / 02 / 26 14:10
理學教學新大樓物理系1F 36102教室
理學教學新大樓物理系1F 36102教室 位於....
Geometrical frustration occurs when interacting degrees of freedom can not match the underlying lattice, and exotic states of matter and novel excitations can emerge. In this talk, I will discuss the fate of two quantum spin liquids on the kagome lattice. First, a preponderance of evidence suggests that the ground state of the nearest-neighbor S = 1/2 antiferromagnetic Heisenberg model on the kagome lattice is a gapless spin liquid. Many candidate materials for the realization of this model possess in addition a Dzyaloshinskii-Moriya (DM) interaction. We study this system by tensor-network methods and deduce that a weak but finite DM interaction is required to destabilize the gapless spin-liquid state. The critical magnitude, D_c/J ~0.012(2), lies well below the DM strength proposed in the kagome material herbertsmithite, indicating a need to reassess the apparent spin-liquid behavior reported in this system [1].

Second, we  study  the topological entanglement entropy and the thermal entropy of a quantum ice model on a geometrically frustrated kagome lattice. We find that the system does not show a Z2 topological order down to extremely low temperature, yet  continues to behave like a classical kagome ice with finite residual entropy. Our theoretical analysis indicates an intricate competition of  off-diagonal and diagonal quantum processes leading to the quasi-degeneracy of states and effectively, the classical degeneracy is restored [2].

[1] C.-Y. Lee, B. Normand, Y.-J. Kao, Phys. Rev. B98, 224414 (2018).
[2] K.-H. Wu, Y.-P. Huang, YJ Kao, Phys. Rev. B99, 134440 (2019).