High-speed kinetic inductive bolometric photoresponse of epitaxial YBa 2 Cu 3 O 7-δ thin films

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Abstract
A general trend is observed in the photoresponse of current biased epitaxial YBa2Cu3O7-(delta ) thin film bridge structures exposed to picosecond laser pulses. Both fast and slow components are seen in the photoresponse near the transition region. The slow component, which has a decay over several nanoseconds, is a resistive bolometric response due to heating of the film by the laser pulse in the resistive transition region. At lower temperatures, only the fast component is observed with an amplitude which is linear with bias current. The fast component has been observed in films ranging in thickness from 30 nm to 260 nm. Using 100 ps, 532 nm laser pulses, the origin of the fast component can be explained by a kinetic inductive bolometric response where the superfluid fraction is rapidly decreased by the laser pulse heating the bridge. Recent results using 5 ps, 820 nm laser pulses on samples maintained at liquid nitrogen temperature (77.4 K) in a high speed measurement setup have revealed fast components in the photoresponse as short as 16 ps full width at half maximum. To our knowledge, this is the fastest photoresponse signal observed to date from YBa2Cu3O7-(delta ) thin films. A large portion of this fast response can be attributed to a kinetic inductive bolometric response. The possibility of a nonbolometric component over this short time scale is discussed.

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