Effect of hydrostatic pressure on the superconducting properties of quasi-1D superconductor K 2 Cr 3 As 3 .

K ₂ Cr ₃ As ₃ is a newly discovered quasi-1D superconductor with a T _c   =  6.1 K and an upper critical field µ ₀ H _c2 (0)  ≈  40 T three times larger than the Pauli paramagnetic limit µ ₀ H _p that is suggestive of a spin-triplet Cooper pairing. In this paper, we have investigated the effects of hydrostatic pressure on its T _c and µ ₀ H _c2 by measuring the ac magnetic susceptibility χ'(T) under magnetic fields at various hydrostatic pressures up to 7.5 GPa. The major findings include: (1) T _c is suppressed gradually to below 2 K at 7.5 GPa; (2) the estimated µ ₀ H _c2 (0) decreases dramatically to below µ ₀ H _p above ~2 GPa and becomes slight lower than the orbital limiting field [Formula: see text] estimated from the initial slope of upper critical field via [Formula: see text]  =  -0.73T _c dH _c2 /[Formula: see text] in the clean limit; (3) the estimated Maki parameter α  =  √2[Formula: see text]/H _p drops from 4 at ambient pressure to well below 1 at P  >  2 GPa, suggesting the crossover from Pauli paramagnetic limiting to orbital limiting in the pair breaking process upon increasing pressure. These observations suggested that the application of hydrostatic pressure could drive K ₂ Cr ₃ As ₃ away from the ferromagnetic instability and lead to a breakdown of the spin-triplet pairing channel. We have also made a side-by-side comparison and discussed the distinct effects of chemical and physical pressures on the superconducting properties of K ₂ Cr ₃ As ₃ .