Fig. 4: Superconducting transition and upper critical field of Re3Ge7−xGax.
a, b Low-temperature resistivity and magnetic susceptibility for Re3Ge7−xGax with 0.2 ≤ x ≤ 0.4, respectively. The vertical dashed line is a guide to the eyes. c Low-temperature specific-heat Cp data for all the Re3Ge7−xGax samples plotted as Cp/T versus T2. The solid lines are fits by the Debye model. d Temperature dependence of normalized electronic specific-heat for the samples with 0.25 ≤ x ≤ 0.35. The back lines are energy conserving constructions to estimate the specific-heat jump and the red line denotes the theoretical BCS curve. e Temperature dependence of resistivity under various fields up to 0.56 T for the sample with x = 0.2, and the field increment is 0.08 T. The horizontal line and arrow indicate the 50% drop of normal-state resistivity and field increasing direction, respectively. f Upper critical field versus temperature phase diagram for the samples with 0.25 ≤ x ≤ 0.35. The solid lines are fits to the data by the Ginzburg–Landau model.
