Thermal Expansion and Magnetostriction of La Metal at Low Temperatures

The thermal expansion of fcc La metal has been measured between 1.5 and 40°K. Below 37°K, the linear expansion coefficient in the normal state is found to be negative, with a minimum of -0.95×${10}^{-6\mathrm{}}$ °${\mathrm{K}}^{-1\mathrm{}}$ at 18°K. This is in contrast with earlier measurements, which were in error. In the superconducting state below 5.59°K, this coefficient is positive, and the extrapolated volume difference $\frac{(V_n-V_s)}{V_n}$ at 0°K is 2.1×${10}^{-6\mathrm{}}$. By means of thermodynamics, the volume effects on the electronic specific heat and on the transition temperature are computed. In agreement with recent results of Smith et al., it is deduced that $T_c$ increases under pressure, and it is shown that this increase can be understood as being due to an increase of the density of states at the Fermi surface.