Abstract

The Kondo-lattice compound CeRh2As2 exhibits an extremely rare case of hosting multiple distinct superconducting (SC) states at a fixed pressure or doping. The SC phase SC1 sets in at the critical temperature Tc ≈ 0.3 K. Applying magnetic field of µ0 H=4 T along the c axis of the tetragonal unit cell triggers a transition into the high-field phase SC2 , the upper critical field of which reaches 15 T ¹. The states SC1 and SC2 have been proposed to have, respectively, even and odd parity of the SC order parameter ². In the absence of magnetic field, the superconductivity is preceded by another ordered state “Phase I” [3,4]. The microscopic nature of Phase I is currently unknown, with magnetic and quadrupolar orders proposed as candidates. The uniqueness of the SC properties of CeRh2As2 has been partially attributed to its atypical crystalline structure, with Ce atoms located in locally non-centrosymmetric environments, while the unit cell has an overall inversion symmetry. Another important ingredient is the exceptionally strong electronic correlations. Together with a pronounced non-Fermi-liquid behaviour, these signal a proximity to a quantum critical point (QCP). Recently, we explored the interplay and relative stability of the ordered states of CeRh2As2 by tuning the material with hydrostatic pressure. We revealed a quantum critical point (QCP) of Phase I at P0 = 0.5 GPa, which is the source of pairing mediating fluctuations and extremely high quasiparticle masses. We also observed a remarkably rapid suppression of the SC phase switching field H* with pressure, with the putative odd-parity SC2 phase becoming the dominant SC state. We discuss this result in the context of the even-odd parity model.

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[2] J. Landaeta et al., Phys. Rev .X, 12 (2022) 031001.

[3] D. Hafner et al., Phys. Rev. X, 12 (2022) 011023.

[4] K. Semeniuk et al., Phys. Rev. B, 107 (2023) L220504 .