Two-phase superconductivity coexisting with unusual orders in the locally non-centrosymmetric CeRh2As2

by Dr Seunghyun Khim (Max Planck Institute for Chemical Physics of Solids, Dresden, Germany)

Wednesday 6 Jul 2022, 15:00 → 16:00 Asia/Shanghai

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Abstract

The recently discovered CeRh₂As₂ superconductor with the transition temperature of T_c = 0.26 K has been attracting attention [1]. Unique upper critical field (H_c2) phase diagrams and a clear thermodynamic phase transition within the superconducting (SC) state evidence a low-field even-parity and a high-field odd-parity state. The two-phase superconductivity can be attributed to the centrosymmetric CaBe₂Ge₂-type structure of CeRh₂As₂ in which the Ce site lacks local inversion symmetry. The local inversion symmetry breaking leads to antisymmetric spin-orbit couplings (ASOC) which have an opposite sign for each sublattice. This allows both the even- and odd-parity SC order parameters that can be switchable from one to another under magnetic fields. We also study the LaRh₂As₂ superconductor in the same crystal structure as CeRh₂As₂, which corroborates the crucial role of Ce-4f electrons in the unusual superconductivity [2,3].

Moreover, the Ce-4f electron in CeRh₂As₂ plays a versatile role to result in emergent phases. As-NQR measurements observed a site-selective line broadening below T_N ~ 0.27 K, suggesting an antiferromagnetic order that coexists with superconductivity [4,5]. In-depth high-field measurements established a rich phase diagram for the in-plane field pointing to the hidden order at T₀ = 0.4 K. This can be explained by a quadrupolar density wave order of the electronic Ce-4f moments [6]. Muon spin relaxation/rotation measurements in various temperatures and magnetic fields characterized anomalous normal-state properties associated with quantum criticality [7].

[1] S. Khim, J. Landaeta et al., Science 373, 1012 (2021);

[2] S. Kimura et al., PRB 104, 245116 (2021);

[3] J. Landaeta et al., to appear in PRB;

[4] M. Kibune et al., PRL 128, 057002 (2022);

[5] S. Kitagawa et al., J. Phys. Soc. Jpn. 91, 043702 (2022);

[6] D. Hafner et al., PRX 12, 011023 (2022);

[7] S. Khim et al., in preparation.

Biography

Dr. Seunghyun Khim received his PhD degree in Seoul National University (SNU) in 2013.  After that, he conducted postdoctoral research first in SNU, then in IFW-Dresden and MPI-CPfS in Dresden, Germany.   In September 2021, he was appointed as a Group Leader in MPI-CPfS, responsible for exploratory synthesis and optimization of growth of novel quantum materials.

Dr. Khim’s research interests include emergent phenomena in strongly correlated and low-D electron systems including superconductivity, Kondo-related physics, and quantum magnetism, exploratory design and synthesis of new material systems, and refinement of single crystal growth to improve in size and quality.

Division

Condensed Matter

Other information

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