Far infrared video detection and difference frequency mixing with tilted c-axis epitaxial YBa2Cu3O7−δ thin films

Abstract

Epitaxial YBa2Cu3O7−δ thin films, grown with a controllable misalignment between c-axis and surface normal, exhibit a sensitive photoresponse to far infrared laser radiation at temperatures below Tc. While no photoresponse was observed in c-axis normal films, a sensitivity of 0.2 V/W was measured at a wavelength of 432 μm for a film with a 20° c-axis tilt. Difference frequency mixing of two laser modes has also been demonstrated at intermediate frequencies between 200 kHz and 6 MHz. Both mixing and video detection are believed to originate in the ac Josephson effect: the effect of the tilted growth is to allow a component of the radiation field to be applied along the c-axis, thus modulating the relatively weak Josephson coupling in this direction.