Enhanced superconductivity in ultrarapidly quenched bulk Al--Cu alloy

Transition temperatures T_c of up to 2.95 °K have been obtained in bulk samples of an aluminum-copper alloy containing 0.85-at.% Cu that had been subjected to the process of ultrarapid quenching. The samples were obtained by a new method of ultrarapid quenching which secures large thin samples that had undergone cooling rates from the melt of about 10⁶ °K sec⁻¹. At the same time, samples conventionally prepared from the same melt showed the normal behavior expected from such an alloy. The rise of T_c is linked to the quenching speed and is proportional to the residual resistance. A possible explanation of the phenomenon is offered by evoking a phonon surface-mode mechanism.