Physics department (Colloquium)

Quantum spin liquids on 2D geometrically frustrated lattice

Speaker : 教授 高英哲 (國立臺灣大學物理系)
Location :
Time : 2021 / 02 / 26 14:10
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).