ENERGY-GAP IN THE OPTICAL-SPECTRUM OF SUPERCONDUCTORS

We study the superconducting gap DELTA which is manifested in optical spectra for frequencies omega much greater than DELTA/hBAR; these freq uencies correspond to the interband transitions. The peak in the diffe rence spectrum of the superconducting and normal phases is predicted, with the peak width being connected to DELTA. The effect is more prono unced for transitions from the heavy-effective-mass band to the light- effective-mass band. Experimental manifestations of the predicted effe ct are discussed.