50 research outputs found
Comparison of the fluctuation influence on the resistive properties of the mixed state of BiSrCaCuO and of thin films of conventional superconductor
The resistive properties of layered HTSC BiSrCaCuO in the mixed state are
compared with those of thin films of conventional superconductors with weak
disorders (amorphous Nb_{1-x}0_{x} films) and with strong disorders
(Nb_{1-x}O_{x} films with small grain structure). The excess conductivity is
considered as a function of superconducting electron density and phase
coherence length. It is shown that the transition to the Abrikosov state
differs from the ideal case both in BiSrCaCuO and Nb_{1-x}O_{x} films, i.e. the
appearance of long-range phase coherence is continuous transition in both
cases. The quantitative difference between thin films with weak and strong
disorders is greater than the one between layered HTSC and conventional
superconductors, showing that the dimensionality of the system, rather than the
critical temperature, is the key factor ruling fluctuation effectsComment: 17 pages, 5 figure
Vortex states in mesoscopic superconducting squares: Formation of vortex shells
We analyze theoretically and experimentally vortex configurations in
mesoscopic superconducting squares. Our theoretical approach is based on the
analytical solution of the London equation using Green's-function method. The
potential-energy landscape found for each vortex configuration is then used in
Langevin-type molecular-dynamics simulations to obtain stable vortex
configurations. Metastable states and transitions between them and the ground
state are analyzed. We present our results of the first direct visualization of
vortex patterns in micrometer-sized Nb squares, using the Bitter decoration
technique. We show that the filling rules for vortices in squares with
increasing applied magnetic field can be formulated, although in a different
manner than in disks, in terms of formation of vortex "shells".Comment: 12 pages, 9 figure