Ultrafast nonbolometric photoresponse of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films

Abstract

Ultrafast transient voltage (<12-ps risetime, 30-ps width) has been measured on a current-biased, very thin (30-nm) YBa/sub 2/Cu/sub 3/O/sub 7-x/ epitaxial film, illuminated by a picosecond laser pulse ( lambda =1.06 mu m) at approximately 50 K. The experimental set-up and the measuring apparatus used allowed precise time measurements. The narrow and high electric pulse obtained is faster than any previously reported. It is attributed to a nonequilibrium Cooper pair breaking process. This first response pulse is followed by a longer bolometric decay interpreted using parameters obtained from measurements taken at smaller fluence and lower temperature as the combination of a phonon escape time and an electron-phonon energy relaxation time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>