## 2021/01/21(Thu) 10:30 -12:00 五樓第一會議室5th Floor(1st meeting room)

Title

Fate of two quantum spin liquids on the kagome lattice

Speaker

Prof. Ying-Jer KaoDepartment of Physics, National Taiwan University

Hosted by

Abstract

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).