Pressure dependence of upper critical field in Ising superconductor 4Hb-TaS₂

The naturally occurring van der Waals heterostructure 4Hb-TaS₂, comprising

alternating insulating and metallic layers, exhibits Ising superconductivity characterized

by an upper critical field that significantly exceeds the Pauli paramagnetic limit.

Furthermore, 4Hb-TaS₂ has been identified as a promising platform for chiral

superconductivity [1], which holds potential for topologically protected quantum

computation. At high temperatures, this compound undergoes charge-density-wave

(CDW) transitions, and the interplay between the CDW and superconducting states

remains elusive.

To explore this relationship, we applied hydrostatic pressure to single crystals of

4Hb-TaS₂. The application of pressure leads to a systematic suppression of the CDW

transition, accompanied by an enhancement of the superconducting critical

temperature Tc. Intriguingly, despite the increase in T_C, the upper critical field

decreases with pressure. Moreover, the temperature dependence of the upper critical

field evolves from an almost linear behavior at low pressure to a nonlinear profile at

high pressure.

These findings indicate a substantial modification of the pairing mechanism under

pressure. Our results demonstrate that pressure serves as an effective tuning parameter

for manipulating the superconducting ground state in this naturally structured

heterostructure. The implications for the relationship between Ising superconductivity

and CDW order will be further discussed.

[1] A. Ribak et al., Sci. Adv. 6, eaax9480(2020)