To reveal the nature of elementary excitations in a quantum spin liquid (QSL), we measured low temperature thermal conductivity and specific heat of 1T-TaS2, a QSL candidate material with frustrated triangular lattice of spin-1/2. The nonzero temperature linear specific heat coefficient γ and the finite residual linear term of the thermal conductivity in the zero temperature limit κ0/T=κ/T(T→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 γ, whereas it enhances κ0/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-TaS2 provides new insights into the influence of quenched disorder on the QSL.
@article{arxiv.1803.06100,
title = {Coexisting localized and itinerant gapless excitations in a quantum spin liquid candidate 1T-TaS$_2$},
author = {H. Murayama and Y. Sato and X. Z. Xing and T. Taniguchi and S. Kasahara and Y. Kasahara and M. Yoshida and Y. Iwasa and Y. Matsuda},
journal= {arXiv preprint arXiv:1803.06100},
year = {2020}
}