Superconducting state in the ternary germanide Y₂AlGe ₃ with related ThCr₂Si₂-type structure

Superconductivity in a ternary germanide, Y₂AlGe₃, was revealed at the transition temperature of 4.5 K by electrical resistivity and magnetic susceptibility measurements. The magnetization versus magnetic field (M-H) curve indicated that Y₂AlGe₃ was a type-II superconductor. The lower critical field H_c1 (0) and the upper critical field H_c2(0) were estimated to be 1.66(8) mT and 1.26(15) T. The coherence length ξ(0)_GL, penetration depth λ(0) _GL, and Ginzburg-Landau (GL) parameter κ(0) obtained from the critical fields were 16.2(5) nm, 631(16) nm, and 38(3), respectively. Specific heat measurements revealed that Y₂AlGe₃ was a weak-coupling BCS superconductor with an isotropic superconducting gap. The electron-phonon mass enhancement parameter λ_γ was calculated to be 0.13, which was in good agreement with the weak-coupling limit inferred from the specific heat ΔC_e=γT_c and 2Δ(0)=k_BT_c.