Competing quantum orders in 6R-TaS₂ revealed by pressure.

Abstract

The transition metal dichalcogenide 6R-TaS₂ is a rich quantum platform hosting charge density wave (CDW) order, superconductivity, and an additional temperature scale at T^* ≃ 40 K marked by pronounced magnetoresistance and a nonlinear Hall effect (NHE). However, the nature of the superconducting pairing, the origin of the NHE, and their relationship with the CDW remain unclear. Using muon-spin rotation, magnetotransport and hydrostatic pressure techniques, we identify a nodal superconducting state with low superfluid density at ambient pressure, with no spontaneous magnetic order detected below T^*. This rules out magnetism as the origin of the NHE. Under pressures up to 2 GPa, the superfluid density rises markedly in correlation with the superconducting transition temperature, the nodal pairing shifts to a nodeless state, and the CDW onset is reduced by half. Notably, the NHE is fully suppressed and magnetoresistance drops by 50% within just 0.2 GPa, highlighting the fragility of the state with NHE. These results reveal competition between superconductivity, charge order, and the nonlinear Hall effect in 6R-TaS₂, driven by weakened interlayer coupling and shared electronic states.