Anisotropic heat conduction in the superconducting state of the quasi-one-dimensional metal Li_0.9Mo₆O₁₇

The quasi-one-dimensional conductor Li_0.9Mo₆O₁₇ superconducts at T_c≅ 2 K with one of the lowest known carrier densities (∽10¹⁷cm⁻³) and a ratio of T_c to Fermi temperature ≥ 0.1, within the BCS-Bose-Einstein-condensation crossover regime.^a A semimetallic state caused by a density-wave-induced Fermi surface reconstruction with highly anisotropic electron and hole pockets is implicated. We present single-crystal, low-T magnetothermal conductivity measurements at Tc with magnetic field perpendicular to the most conducting plane. For heat current along the chains, the thermal conductivity at fixed T increases as a simple power law in field up to H_c2, attributable to a small charge-carrier contribution. For heat current transverse to the chains the thermal conductivity decreases with field. The implications of these observations for superconducting gap anisotropy will be discussed.

^a J. L. Cohn et al., Phys. Rev. B 108, L100512 (2023).