Electromagnetic Generation of Transverse Acoustic Waves in the Gigahertz Range Using Indium Films

Transverse acoustic waves were generated electromagnetically at 9 GHz using In films with a conversion efficiency $\alpha$ of 5 × ${10}^{-5\mathrm{}}$. A good agreement is found between theory and experiment and we obtain the value of 620 Å for the superconducting penetration depth $\lambda$ at $0.4T_c$ and 5×${10}^{10}$ ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ for the ratio of the conductivity to the mean free path for In. From the temperature dependence of $\alpha$ below the superconducting transition temperature it is concluded that pair scattering at the surface does not conserve momentum.