Wydarzenia

Seminarium Oddziału Badań Magnetyków

CeRh2As2: from horizontal flux growth to new experimental findings

dr Grzegorz Chajewski

Oddział Badań Magnetyków, INTiBS PAN

Since the discovery of unconventional superconductivity in CeRh2As2 [1], there has been tremendous excitement in the condensed matter research community to explore the various intriguing aspects of this material. The most remarkable feature of the compound is related to the phase transition within the superconducting state, which occurs upon applying a magnetic field along the c-axis and leads to an extraordinary violation of the Pauli-Clogston limit. It makes CeRh2As2 one of the only few known multi-phase heavy-fermion superconductors. The other peculiarity is the puzzling T0-anomaly observed at temperatures slightly above the superconducting state of the material and tentatively ascribed to the emergence of a unique quadrupole density wave state. Despite extensive and intensive research on this material, there is still no decisive explanation for the nature of the physical mechanism responsible for the phase transition within the superconducting state of CeRh2As2 and the origin of the T0-anomaly. This motivates scientists to pursue further investigations into the compound.
In our meticulous specific heat studies performed on the recently synthesized new generation of high-quality single-crystalline samples [2], we detected a previously unobserved feature of the compound, namely the first-order phase transition [3]. Using a set of various measurement approaches, we precisely traced its magnetic-field evolution and concluded on its magnetic character. We found that it is observed solely for magnetic fields applied along the c-axis and within the low-field superconducting state, it emerges well below the critical temperature Tsc. In turn in higher fields, it seems to merge with the superconducting phase transition.
Furthermore, our measurements performed with a field applied along the a-axis indicated the change of the character of the superconducting phase transition from second-order type to first-order one. This resembles the effect observed in e.g. CeCoIn5 [4] and Ce2PdIn8 [5], attributed to the possible emergence of low-temperature high-field FFLO (Fulde-Ferrell-Larkin-Ovchinnikov) state.
Based on our experimental findings and drawing parallels to antiferromagnetic heavy-fermion superconductors CeRhIn5 and Ce2RhIn8, we present an alternative interpretation of the physical behavior of CeRh2As2, markedly distinct from the previously suggested quadrupole density wave scenario.
[1]: S. Khim et al., Science 373 (2021) 1012.
[2]: G. Chajewski et al., Mater. Horiz., 11 (2024) 855.
[3]: G. Chajewski et al., Phys. Rev. Lett., 132 (2024) 076504.
[4]: A. Bianchi et al., Phys. Rev. Lett. 91 (2003) 187004.
[5]: Y. Tokiwa et al., Phys. Rev. B 84 (2011) 140507.