Fig. 6.

Relation between transition temperature and $\gamma$ coefficient. a Superconducting transition temperature $T_{\mathrm{c}}$ as a function of Al content. Note that $T_{\mathrm{c}}$ shows the sharp drop at Al content of about 15% corresponding to the QC and the 2/1AC. b Electronicspecific heat coefficient $\gamma$ as a function of Al content. The slight drop at 15% Al content suggests the pseudogap formation. c Correlation between $T_{\mathrm{c}}$ and $1∕\gamma$. The straight line denotes the interrelationship, $ln{T}_{\mathrm{c}}\propto 1∕\gamma$, marking the constant pairing interaction