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  • Letter
  • Open Access

Phase diagram of CeRh2As2 for out-of-plane magnetic field

P. Khanenko1,*, J. F. Landaeta1,2, S. Ruet1, T. Lühmann1, K. Semeniuk1, M. Pelly3, A. W. Rost3, G. Chajewski4, D. Kaczorowski4 et al.

C. Geibel1, S. Khim1, E. Hassinger2, and M. Brando1,†

  • *Contact author: pavlo.khanenko@cpfs.mpg.de
  • †Contact author: manuel.brando@cpfs.mpg.de
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Phys. Rev. B 112, L060501 – Published 8 August, 2025

DOI: https://doi.org/10.1103/gt54-tvc2

Abstract

The heavy-fermion superconductor (SC) CeRh2As2 (Tc = 0.35 K) shows two 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 have indicated that the change in SC order parameter detected at μ0H*≈4T is due to strong Rashba spin-orbit coupling at the Ce sites caused by the locally noncentrosymmetric environments of the otherwise globally centrosymmetric crystalline structure. Another phase (phase I) exists in this material below T0 = 0.54 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 μ0H0≈6T, larger than H*. 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 because the T0(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 H0 inside the SC2 phase and confirm our previous prediction. Furthermore, we observe the transition across the T*(H) line in T-dependent specific heat measurements, which show that the T*(H) line is not perpendicular to the field axis but has a positive slope. Our findings support recent muon spin resonance results which suggest coexistence of phase I with SC.

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Phys. Rev. B 112, L060501– Published 8 August, 2025
  • Received 22 April 2025
  • Revised 4 July 2025
  • Accepted 9 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by Max Planck Society.

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