Phase-Slip Centers and Their Interactions.
We have performed a series of experiments in order to measure the diffusion length (LAMDA)(,Q*) of the quasiparticle charge generated in a phase-slip center (PSC) and to detect the oscillations of the supercurrent in the PSC. Three types of samples were fabricated photolithographically: samples of types S, type T and type M. In samples of type S, consisting of long tin microbridges (40(mu)m x 1(mu)m x 0.1(mu)m) with four sides probes, we measured the effects of the quasiparticle current generated in one PSC on the appearance of other PSCs in the same microbridge. The nucleation of PCSs was controlled by applying current through the side probes to different segments of the microbridge. In that way the interaction effects could be measured as a function of the distance between the two interacting PSCs. We separated heating effects from diffusive current effects and we observed the exponential decay of the quasiparticle current with the distance from the PSC source. We found that the chracteristic length corresponds to a relaxation time (tau)(,Q*)=(7 (+OR-) 2) x 10('-10) sec at T = 0.99T(,c). From the heating effect data we determined that the heat transfer coefficient is (alpha) = 1.5 watt/K cm('2) for our samples on glass substrates and in direct contact with the liquid He bath. In samples of type T, consisting of long tin microbridges (40(mu)m x 1(mu)m x 0.1(mu)m) with four normal tunnel junctions probes we measured the quasiparticle potential. We found that this potential decays exponentially from the center of the PSC and that the characteristic decay length diverges at the critical temperature T(,c) corresponding to a relaxation time (tau)(,Q*)(T) = (0.7 (+OR-) 0.2) x 10('-10)sec(1-T/T(,c))('- 1/2).We also measured the nonequilibrium potential induced by a normal current injected through one of the probes and the effect of that normal current on the appearance of the first PSC in the microbridge. From those injection experiments we also obtained a value of ('(LAMDA))(,Q*), with agrees with our previous results on the same samples. From the experimental magnitude of (tau)(,Q*) in samples of type S and of type T, we determined the inelastic phonon scattering time (tau)(,E) and found that, close to T(,c), (tau)(,E)=(1.6 (+OR-) 0.4) x 10(' -10) sec in tin. Samples of type M consist of tin microbridges of various lengths. The effect of microwave radiation on the I-V curves of these samples was investigated. We observed Josephson steps in some of those samples, proving the presence of oscillations of the supercurrent in the core of the PSC.
- Pub Date:
- Physics: Condensed Matter