Universal scaling of the heat capacity in a quantum spin liquid state of 1T-TaS₂

To elucidate the nature of quantum spin liquid (QSL), it is important to understand the effect of randomness on QSL. Here, we have investigated the low energy excitations on pure, Se-substituted and electron-irradiated 1T-TaS₂, a QSL candidate material with spin-1/2 on a triangular lattice[1, 2], by measuring low-temperature thermal conductivity and heat capacity. Finite residual linear terms of thermal conductivity, κ/T(T→0), in pure 1T-TaS₂ indicates the presence of itinerant gapless excitations. The magnetic contribution of the heat capacity of 1T-TaS₂ and 1T-TaS_2−xSe_x well obeys a universal scaling relation, consistent with a theory that assumes the presence of localized orphan spins forming random singlets[3]. These results capture a microscopic picture of the QSL, in which localized orphan spins induced by disorder are surrounded by itinerant spinon that forms Fermi surface. On the other hand, electron irradiation in 1T-TaS₂, which introduces strong quenched disorders in Ta-layers, changes the scaling function dramatically, suggesting a possible new state of spin liquid.
[1] K. T. Law, et al., PNAS 110, 6996-7000 (2017).
[2] M. Klanjsek, et al., Nature Physics 13, 1130 (2017).
[3] I. Kimchi, et al., Nature Communication 9, 4367 (2018).
[4] H. Murayama, et al., arXiv:1909.00583.