Abstract
To reveal the nature of elementary excitations in a quantum spin liquid (QSL), we measured low temperature thermal conductivity and specific heat of 1T-TaS$_2$, a QSL candidate material with frustrated triangular lattice of spin-1/2. The nonzero temperature linear specific heat coefficient $\gamma$ and the finite residual linear term of the thermal conductivity in the zero temperature limit $\kappa_0/T=\kappa/T(T\rightarrow 0)$ are clearly resolved. This demonstrates the presence of highly mobile gapless excitations, which is consistent with fractionalized spinon excitations that form a Fermi surface. Remarkably, an external magnetic field strongly suppresses $\gamma$, whereas it enhances $\kappa_0/T$. This unusual contrasting behavior in the field dependence of specific heat and thermal conductivity can be accounted for by the presence of two types of gapless excitations with itinerant and localized characters, as recently predicted theoretically (I. Kimchi et al., arXiv:1803.00013 (2018)). This unique feature of 1T-TaS$_2$ provides new insights into the influence of quenched disorder on the QSL.
Highlights
A spin liquid is a state of matter in which the spins are correlated yet fluctuate strongly, like in a liquid, down to very low temperatures
These results appear to capture an essential feature of the quantum spin liquid (QSL) state of 1T-TaS2; localized orphan spins induced by disorder form random valence bonds and are surrounded by a QSL phase with spinon Fermi surface
To reveal the nature of the QSL state in 1T-TaS2 with the 2D perfect triangular lattice, we investigate the effect of randomness due to quenched disorder through the systematic measurements of heat capacity and thermal conductivity in pure, Se-substituted, and electron-irradiated crystals
Summary
A spin liquid is a state of matter in which the spins are correlated yet fluctuate strongly, like in a liquid, down to very low temperatures. Transition metal dichalcogenide 1T-TaS2 has aroused great interest as a candidate material that hosts a QSL ground state on the 2D perfect triangular lattice [28] To obtain new insights into low-lying spin excitations of 1T-TaS2, the effect of randomness induced by quenched disorder on the spin liquid state is investigated. For this purpose, we performed systematic studies of lowtemperature heat capacity and thermal conductivity on pure, Se-substituted and electron-irradiated crystals of 1T-TaS2. Introduction of strong disorder by electron irradiation leads to a possible new state of a spin liquid
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