Coexistence of ordered states and two-phase superconductivity in the heavy-fermion superconductor CeRh2As2
일 시 : 2022년 04월 19일 화요일 14:00
연 사 : 김 승 현 박사 (MPI-Dresden)
장 소 : 자연과학관 226호 & 온라인 ( 회의 ID: 893 6038 1750 , 암호: 164860 )
초 록
The recently discovered CeRh2As2 has been attracting attention to the unusual two-phase superconductivity [1]. A clear thermodynamic phase transition at 4 T within the superconducting (SC) state separates it into a low- and high-field phase. Strong Pauli-paramagnetic pair breaking in the low-field phase and an enhanced upper critical field (Hc2) of the high-field phase indicate a field-induced transition between an even- to odd-parity SC order parameter. CeRh2As2 has the centrosymmetric CaBe2Ge2-type structure which lacks local inversion symmetry at the Ce site. This gives rise to antisymmetric spin-orbit couplings that allow the two distinct SC phases of which the even-parity phase is favored over the odd-parity phase in the zero magnetic field. An external field of 4 T then switches a dominating SC order parameter from one to another to result in the unique Hc2 phase diagram.
There are recent experimental achievements that revealed intriguing normal state properties reflecting another aspect of the Ce-4f electrons. As-NQR measurements observed a site-selective line broadening below TN ~ 0.27 K, suggesting an antiferromagnetic order in the superconducting state [2,3]. In-depth high-field measurements established a rich phase diagram of the unknown hidden order at T0 = 0.4 K, which is claimed to be the quadrupolar density wave order of the electronic Ce moments [4]. Muon spin relaxation/rotation measurements were performed to identify the nature of TN and T0 as well as the strange-metal behavior [5].
[1] S. Khim, J. Landaeta et al, Science 373, 1012 (2021).
[2] M. Kibune et al., Phys. Rev. Lett. 128, 057002 (2022).
[3] S. Kitagawa et al., J. Phys. Soc. Jpn. 91, 043702 (2022).
[4] D. Hafner et al., Phys. Rev. X 12, 011023 (2022).
[5] S. Khim et al., in preparation.