Spin-Excitations of 1T-TaS2 and Related Magnetoresistance in the 4Hb Phase

Spin-spin interactions can lead to exotic ground states with emergent excitations in frustrated quantum magnets. Such a system is the transition metal dichalcogenide TaS₂. While the 1T phase of the material is electrically insulating and exhibits no magnetic ordering down to millikelvin temperatures, the specific heat has a linear fermionic-type contribution that suggests a large bandwidth. The magnetic torque is strongly anisotropic and has a singular response at low magnetic fields which we attribute to a continuous disassociation of singlet pairs. This picture is also supported by the perfect collapse of the specific heat data at various temperatures and magnetic fields onto a universal curve predicted for singlets with a random distribution of antiferromagnetic coupling strengths. We interpret our data in the framework of a quantum spin liquid ground state having a large bandwidth with minority spins forming an array of singlet pairs with a continuum of coupling constants. Moreover, by intercalating layers of the proposed spin liquid 1T phase with superconducting layers of 2H phase we observe surprising anisotropic magnetoresistance, possibly reminiscent of the spin interactions in the 1T phase.