Ultrafast photoresponse in microbridges and pulse propagation in transmission lines made from high-T/sub c/ superconducting Y-Ba-Cu-O thin films

Abstract

We report our femtosecond time-resolved measurements of the photoresponse of microbridges in YBa2Cu3O70x (YBCO) thin films, performed using an electrooptic sampling technique. Our test structures consisted of 5-m-wide, 7-m-long microbridges, incorporated in 4-mm-long coplanar waveguides, fabricated in 100-nm-thick, high-quality epitaxial YBCO films grown on LaAlO3 substrates by laser deposition. When varying the biasing conditions between the superconducting and switched states, we observed transients of single-picosecond duration that corresponded to the nonequilibrium kinetic-inductance and the electron-heating response mechanisms, respectively. In both cases, experimental waveforms could be accurately simulated using a nonequilibrium (two-temperature) electron-heating model. From the fits, the YBCO intrinsic temporal parameters associated with the nonequilibrium conditions were extracted. The electron thermalization time was found to be 0.56 ps in the state above the material's critical temperature (T c = 89 K) and 0.9 6 0.1 ps in the superconducting state at temperatures ranging from 20 to 80 K. The electron-phonon energy relaxation time was found to be 1.1 ps. The single-picosecond pulse distortion due to propagation on a YBCO coplanar waveguide was also studied. Our results show that a YBCO microbridge can intrinsically operate as a photodetector at rates exceeding 100 Gb/s, making it useful as an optical-to-electrical transducer for optoelectronic interfaces in YBCO digital electronics. Simultaneously, YBCO mixers, based on hot-electron effects, should exhibit an intrinsic bandwidth exceeding 100 GHz.

Magnetoresistivity of thin YBa2Cu3O7−δ films on sapphire substrate

“…Energy relaxation rates in the range of only a few picoseconds have been measured from optical to infrared wavelengths [1]- [3].…”

Investigating Optoelectronic Properties of the NbN Superconducting Nanowire Single Photon Detector

“…We suspect that the electrically shared ground of the analog and digital parts in the source meter is responsible for the difference. (Lindgren et al, 1996). The values of R s by small signal RF/microwave measurement results in less than 20 Ω,e v e nw h e nI b is 0.5 µAl e s st h a nI c (28.5 µA in this case), which is much lower than the stable resistance of a hotspot by Joule heating.…”

“…In addition, the scanning direction depends on whether it starts from a higher bias voltage down to zero (backward), or vice versa (forward). Within the switched states as defined in (Lindgren et al, 1996), the nanowire will exhibit a hysteresis I-V curve due to the thermal healing of the hotspot, i.e. the voltage scans of the forward and backward mode show the hysteresis behavior; and the measured current remains at the level of latching current until the bias voltage decreases below the forward latching voltage point.…”

“…T h efi r s t regime is the superconducting regime and the slope of I-V curve is primarily determined by the cryogenic cable resistance; The second is the switching state (Lindgren et al, 1996), in which spontaneous thermo-electrical relaxation oscillations is dominantly observed; The third regime is the formation and expansion of a stable hotspot, which is the starting point of a self-heating effect. The hotspot grows up with the increment of dc bias to occupy one entire segment of the nanowire.…”

“…5 (a) prior and after the critical current I c point, is the superconducting and switched state (Lindgren et al, 1996), respectively. For the latter, it is characterized by a spontaneous relaxation oscillation at about 800 KHz counting rate, when we use the method to perform photon/dark count characterization in (Yan et al, 2009 (Kampwirth & Gray, 1981) estimated about the single granular size of 100 nm.…”