Conventional type-II superconductivity in locally noncentrosymmetric LaRh2 As2 single crystals

We report on the observation of superconductivity in LaRh2As2, which is the analog without f electrons of the heavy-fermion system with two superconducting phases CeRh2As2 [S. Khim, Science 373, 1012 (2021)10.1126/science.abe7518]. A zero-resistivity transition, a specific-heat jump, and a drop in magnetic ac susceptibility consistently point to a superconducting transition at a temperature of Tc=0.28 K. The magnetic-field temperature superconducting phase diagrams determined from field-dependent ac-susceptibility measurements reveal small upper critical fields μ0Hc2≈12 mT for H∥ab and μ0Hc2≈9 mT for H∥c. The observed Hc2 is larger than the estimated thermodynamic critical-field Hc derived from the heat-capacity data, suggesting that LaRh2As2 is a type-II superconductor with Ginzburg-Landau parameters κGLab≈1.9 and κGLc≈2.7. The microscopic Eliashberg theory indicates superconductivity to be in the weak-coupling regime with an electron-phonon-coupling constant λe-ph≈0.4. Despite a similar Tc and the same crystal structure as the Ce compound, LaRh2As2 displays conventional superconductivity, corroborating the substantial role of the 4f electrons for the extraordinary superconducting state in CeRh2As2.