Phonon Spectrum of La

Observed phonon structure in the tunneling density of states of superconducting La films ($T_c={4.9}^{\circ }\mathrm{K}$, $\frac{2\Delta }{k{T}_c}=3.8\mathrm{}$) contains resolvable detail not reported previously, with maximum deviations from the BCS prediction amounting to 1.7%. The McMillan-Rowell method of analysis produces a phonon spectrum ${\alpha }^{2}F\left(\omega \right)$ characterized by parameters which predict $T_c=5.0\mathrm{}$ °K via the McMillan equation. Implications of this agreement are discussed.