Wavelength Dependence of the Photoresponse of a Yttrium-Barium-Copper-Oxide Thin Film

The work explores the wavelength dependence of the photoresponse of an underdoped YBa2Cu3O7-? thin film with a sharp resistive transition. The nature of the photoresponse is studied at a time scale of ~ 1 s, varying the excitation wavelength while holding sample temperature constant within the superconducting-normal transition. The bolometric portion of the photoresponse is then accounted for, and the residual non-bolometric response is compared to that found in other doping regimes and time scales. The observed wavelength dependence of the excess conductance is most likely caused by excitations into the conduction band from the filled copper bands in the CuO2 plane layer of the crystal.