The phase diagram of CeRh${}_2$As${}_2$ for out-of-plane magnetic field

Abstract

The heavy-fermion superconductor CeRh${}_2$As${}_2$ ($T_{\text{c}}=0.35\text{K}$) shows two superconducting (SC) phases, SC1 and SC2, when a magnetic field is applied parallel to the $c$ axis of the tetragonal unit cell. All experiments to date indicate that the change in SC order parameter detected at ${\mu }_{\text{0}}{H}^{\ast }\approx 4\text{T}$ is due to strong Rashba spin-orbit coupling at the Ce sites caused by the locally non-centrosymmetric environments of the otherwise globally centrosymmetric crystalline structure. Another phase (phase I) exists in this material below $T_{\text{0}}=0.54\text{K}$. In a previous specific heat study [K. Semeniuk et al. Phys. Rev. B, $107$, L220504 (2023)] we have shown that phase I persists up to a field ${\mu }_{\text{0}}{H}_0\approx 6\text{T}$, larger than $H^{\ast }$. From thermodynamic arguments we expected the phase-I boundary line to cross phase SC2 at a tetracritical point. However, we could not find any signature of the phase-I line inside the SC2 phase and speculated that this was due to the fact that the $T_0(H)$ line is almost perpendicular to the $H$ axis and, therefore, invisible to $T$-dependent measurements. This would imply a weak competition between the two order parameters. Here, we report magnetic field dependent measurements of the magnetostriction and ac-susceptibility on high-quality single crystals. We see clear evidence of the singularity at $H_0$ inside the SC2 phase and confirm our previous prediction. Furthermore, we observe the transition across the $T^{\ast }(H)$ line in $T$-dependent specific heat measurements, which show that the $T^{\ast }(H)$ line is not perpendicular to the field axis, but has a positive slope. Our work supports recent $\mu$SR results which suggest coexistence of phase I with superconductivity.

9 pages, 11 figures, includes supplemental material

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Cited by in corpus (6)

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• Unveiling the superconducting scenario in multiphase superconductor CeRh${}_2$As${}_2$ from space-group symmetry analysis and DFT calculations
• Multipolar fluctuations from localized 4f electrons in CeRh2As2
• La substitution studies on the heavy-fermion superconductor CeRh${}_2$As${}_2$
• Quasiclassical theory of vortex states in locally non-centrosymmetric superconductors: application to CeRh${}_2$As${}_2$
• Composite Superconducting Orders and Magnetism in CeRh${}_2$As${}_2$