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TT: Fachverband Tiefe Temperaturen

TT 41: Unconventional Superconductors

TT 41.11: Vortrag

Mittwoch, 18. März 2020, 18:00–18:15, HSZ 201

Field-induced change of the superconducting state in the locally non-centrosymmetric heavy fermion CeRh₂As₂ — •Javier Landaeta, Seunghyun Khim, Daniel Hafner, Jacinta Banda, Manuel Brando, Robert Küchler, Christoph Geibel, and Elena Hassinger — Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany

CeRh₂As₂ is a new heavy fermion superconductor with a CaBe₂Ge₂-type crystalline structure, which lacks inversion symmetry locally at the Ce site. A weak phase transition is observed in the specific heat at T₀=0.4 K with possibly quadrupolar origin and below T_c= 0.27 K the material becomes superconducting. Here, we present a comprehensive study of the low temperature AC magnetic susceptibility in a single crystal of CeRh₂As₂ up to 15 T. We did not detect any additional transition above T_c, supporting that the specific heat anomaly might be caused by a quadrupolar order. The superconducting upper critical field is strongly anisotropic with µ₀H_c2= 13 T for B∥ c and µ₀H_c2= 2 T for B⊥ c, which exceed the Pauli limit. The large H_c2 and their anisotropy are reminiscent of non-centrosymmetric superconductors such as CePt₃Si, CeRhSi₃, CeIrSi₃. What makes CeRh₂As₂ stand out is its unique superconducting phase diagram with a pronounced kink at 4 T for B∥ c reproducible in heat capacity, resistivity and AC susceptibility measurements. Moreover, isothermal AC susceptibility and magnetostriction reveal a sharp phase transition inside the superconducting phase at 4 T independent of temperature. Therefore, two different superconducting states exist for B∥ c in CeRh₂As₂.