Abstract
Transverse acoustic waves were generated electromagnetically at 9 GHz using thin films of tin, gold, and copper on silicon substrates. We report measurements of the conversion efficiency α of electromagnetic into acoustic energy as a function of temperature and film thickness at and below 4.2 K and preliminary results at liquid-N2 temperature. The highest conversion efficiencies found at 4.2 K for Sn and Au were 1 × 10-5 and 2.5 × 10-5, respectively. In the temperature range of 1.4-4.2 K, the values of α for normal metals were found to be practically temperature as well as microwave-power independent. The value of α for superconducting tin decreases strongly below the superconducting transition temperature and becomes magnetic field and microwave-power dependent. This is in agreement with our previous results on indium. Using gold films we measured the thickness dependence of α in the range of π<q d<4π, where q is the acoustic wave number in the metal in d is the film thickness. We find a pronounced maximum at q d=2π and indications for another maximum at q d=4π. The values of α at 4.2 K as well as the temperature and thickness dependence of α are found to be in good agreement with the theory based on diffuse surface scattering of the conduction electrons.
Original language | English |
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Pages (from-to) | 1499-1505 |
Number of pages | 7 |
Journal | Physical Review B |
Volume | 9 |
Issue number | 4 |
DOIs | |
State | Published - 1974 |