Quantum spin liquid (QSL) is a state of matter where strong quantum fluctuations destroy the long-range magnetic order even at zero temperature. In two-dimensional triangular lattice antiferromagnet, such as organic insulators, possible QSL states have been reported. However, detailed properties remain unclear due to lattice distortion and strong spin-orbit coupling.
Recently, 1T-TaS₂ is proposed as an ideal material for QSL [1]. It becomes commensurate charge-dansity wave state and Mott-insulating state below 60 K, in which S=1/2 spin is localized on a center of cluster composed of 13 Ta atoms and arranged on perfect triangular lattice. NQR and μSR reveal the absence of magnetic order down to 70 mK [2].
We performed the measurements of thermal conductivity κ and specific heat C to study low-energy quasiparticle excitations. κ/T and C/T show residual term as T → 0, demonstrating the presence of gapless spin excitations. In stark contrast to organic compounds, quasiparticle mean free path is largely enhanced by applying magnetic field.
References
[1] K. T. Law, et al., PNAS 110, 6996-7000 (2017).
[2] M. Klanjsek, et al., arXiv:1704.06450v1 (2017).