Pressure Control of Intertwined Quantum Orders in 6R-TaS₂

The transition metal dichalcogenide 6R-TaS₂ offers a natural platform for studying the interplay between charge density wave (CDW) order, superconductivity, and transport anomalies. Recent results show that, in the intermediate temperature range between charge order and superconductivity, an additional characteristic temperature scale emerges at T*=40 K, marked by pronounced magnetoresistance and an anomalous contribution to the Hall effect (ACH). However, the nature of the superconducting pairing, the origin of ACH, and their relationship with the CDW remain unclear. Using muon-spin rotation (μSR), magnetotransport, scanning tunnelling microscopy/spectroscopy (STM/STS) and hydrostatic pressure techniques, we identify a nodal superconducting state with low superfluid density at ambient pressure [1], with no spontaneous magnetic order detected below T*. This rules out magnetism as the origin of the ACH. 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 ACH is fully suppressed and magnetoresistance drops by 50% within just 0.2 GPa, highlighting the fragility of the state with ACH. These results reveal an unconventional superconducting pairing in 6R-TaS₂, competing with both CDW and ACH through the weakened interlayer coupling and competition for the same electronic states. With this multifaceted approach, we establish a comprehensive phase diagram that reveals the intricate interplay and competition between the intertwined quantum orders in 6R-TaS₂.

[1] V. Sazgari et. al. and Z. Guguchia, arXiv:2503.13944 (2025).