Competing Quantum Orders in 6R-TaS${}_2$: Unconventional Superconductivity, Charge Order, and an Anomalous Hall Effect phase

Abstract

The transition metal dichalcogenide 6R-TaS${}_2$ offers a natural platform for studying the interplay among charge density wave (CDW) order, superconductivity, and transport anomalies. Recent findings reveal that, in the intermediate temperature range between charge order and superconductivity, a hidden order emerges around $T^{\ast }$ $\simeq$ 35 K-as evidenced by strong magnetoresistance and an anomalous Hall effect (AHE). However, the nature of the superconducting pairing, the hidden order, and their relationship with the CDW remain unclear. Using $\hat{I}¼$SR, magnetotransport, susceptibility, and hydrostatic pressure techniques, we identify a nodal superconducting state with low superfluid density at ambient pressure, with no spontaneous magnetic order detected below $T^{\ast }$. This indicates that the AHE originates from the band structure rather than magnetism. 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, AHE is fully suppressed and magnetoresistance drops by 50$\%$ within just 0.2 GPa, highlighting the fragility of the hidden order. These results reveal an unconventional superconducting pairing in 6R-TaS${}_2$, competing with both CDW and hidden orders through weakened interlayer coupling and competition for the same electronic states. With a multifaceted approach, we establish a comprehensive phase diagram that reveals the intricate interplay and competition between the intertwined quantum orders in 6R-TaS${}_2$.

12 pages, 9 Figures