Pressure-Induced Superconductivity in ${\mathrm{CaLi}}_2$

A search for superconductivity has been carried out on the hexagonal polymorph of Laves-phase ${\mathrm{CaLi}}_2$, a compound for which Feng, Ashcroft, and Hoffmann predict highly anomalous behavior under pressure. No superconductivity is observed above 1.10 K at ambient pressure. However, high-pressure ac susceptibility and electrical resistivity studies to 81 GPa reveal bulk superconductivity in ${\mathrm{CaLi}}_2$ at temperatures as high as 13 K. The normal-state resistivity displays a dramatic increase with pressure.

Figure 1

Electrical resistance versus temperature for ${\mathrm{CaLi}}_2$ (sample $A$) at pressures 8, 11, 26, 36, 45, 52, 74, 81, 46, taken in that order. Inset shows data plotted as resistance normalized at 16 K versus temperature to 17 K; dots bridge gap in data at 26 and 36 GPa.

Figure 2

Real part of ac susceptibility versus temperature for ${\mathrm{CaLi}}_2$ (sample $B$) for pressures 25, 35, 39, 43, 47, 54, taken in that order. In the inset, the superconducting transition for 39 GPa pressure shifts by 0.62 K to lower temperatures in 500 Oe dc magnetic field.

Figure 3

Superconducting transition temperature $T_c$ of ${\mathrm{CaLi}}_2$ versus pressure from resistivity ($\circ$) and ac susceptibility ($⧫$) measurements in Figs. 1, 2. Value of $T_c$ is determined from transition midpoint; vertical “error bars” give 20–80 transition width. Horizontal “error bars” reflect width of $R_1$ ruby peak. Primed and unprimed numbers give order of measurement. Broad gray line is a guide to the eye.