Paper 9 ACOUSTIC WAVES (Acoustic wave propagation in crystals, glasses, spurious media, and periodic structures)

Nonlinear acoustoelectron effects in superconductors. Yu.V.Ilisavslui, E.Z.Yakhkind (RAS, Ioffe Physical Techcal Institute, StPetersburg, 19402 1, Russia).

The new experimental approach in superconductor physics - nonlinear acoustics of superconductors - is developed. In contrast with former investigations in which mainly the effect of superconductivity on acoustic wave propagation was studied this work has to do with inverse process - namely with the influence of an acoustic wave on superconductors. Using in the experiments of highly intensive (up to 5xlOE4 Wt/cmE2) surface acoustic waves (SAW) permits us to obtain a strong nonlinearity of acoustoelectron interaction in thin superconducting films deposited on appropriate substrates. To make the measurements more informative both usual (Pb) and HTSC (YBCO) superconductors are studied. Four problems are now under study.

1. As preliminary experiments show in the case of lead films the SAW effect on superconducting state results in substantial decrease (a few tenths of degree) of superconducting transition temperature Tc with spatial and temporal periodicity of SAW. Depending on essential parameters of superconductors this effect makes it possible to study peculiarities of the superconducting state of different materials (including kinetic characteristics). 2. Investigations of the acoustoelectric effect in layered structure YZ-LiNb03 - thin film YBa2Cu307-x are in progress. Depending directly on electronic properties of the superconductor this effect is of great importance for understanding of the mechanism of the superconductivity. It is found that above Tc the behavior of the acoustoelectric voltage Vae is typical for metallic p-type conductors. However below Tc Vae changes its sign that makes a challenge to the theory. 3. A study is made of the influence of an external magnetic field on the above mentioned processes. Such measurements give valuable information about vortex motion. 4. As our experiments show the deformation wave form has D-shape profile at hgh acoustic power level. These data can serve as a basis for development of the strong elastic non-linearity theory for layered structures.

REFERENCE 1,Dyakonov K.V, Ilisavskii Y.V., Yakhkind E.Z. The action of sound on superconducting state of thin lead films. Pisma v zhumal tekhnichecheskoi fiziki, 1988,14,2249-2253.

2. Ilisavskii Y.V., Yakhkind E.Z., Go1 man E.K., Mitrofanov A.P. Acoustoelectric effect of superconducting YBazCu307-[ films. JETP Letters (Pisma v zhumal eksperimentalnoi i teoretichescoi fizilu), 1990,52,1138-1141.

3. Ilisavskii Y.V., Yakhkind E.Z., Gol*man E.K., Karmanenko S.F. Acoustoelectronic interaction in superconducting YBa2Cu307-[ films. Fizlka Tverdogo Tela, 199 1,33,824-829.

4. Goltsev A.V., Dyakonov K.V., Ilisavskii Y.V., Yakhkind E.Z. Acoustic investigations as method for a study of the anisotropy of Fermi surface and of superconducting gap. Akusticheskii zhumal, 1993 (in print).