Effect of Pressure on Superconducting Transitions and on Electrical Resistance at Low Temperatures

Measurements have been made on the shift of the superconducting transition temperatures of Sn, In, Hg, Tl, and Ta by pressures up to 5000 kg/${\mathrm{cm}}^2$. For thallium, $\frac{\Delta T_c}{\Delta P}$ is initially positive but becomes negative above 1200 kg/${\mathrm{cm}}^2$. The effect of pressure on the normal resistance of all these metals, except Hg, has been investigated just above their transition temperatures. In all cases the resistance decreases under pressure.