  Transport properties of a superconductor-semiconductor-superconductor
(S-Sm-S) junction with superlattice structure are investigated. Differential
resistance as a function of voltage shows oscillatory behavior under the
irradiation of radio-frequency (RF) waves with the specific frequency of 1.77
GHz regardless of the superconducting materials and the junction lengths.
Experimental data are quantitatively explained in terms of the coupling of
superconducting quasiparticles with long-wavelength acoustic phonons indirectly
excited by the RF waves. We propose that the strong coupling causes the
formation of novel composite particles, Andreev polarons.
