Matemaatilise füüsika võrrandid

https://www.ester.ee/record=b5203202*es

Band filling effects on coherence lengths and penetration depth in the two-orbital negative-U Hubbard model of superconductivity

The two-orbital superconducting state is modeled by on-site intra-orbital negative-U Hubbard correlations together with inter-orbital pair-transfer interactions. The critical temperature is mainly governed by intra-orbital attractive interactions and it can pass through an additional maximum as a function of band filling. For the certain number of electrons the clear interband proximity effect is observable in the superconducting state of the band with a smaller gap. The influence of band fillings and orbital site energies on the temperature dependencies of two-component superconductivity coherence lengths and magnetic field penetration depth is analyzed. The presence of proximity effect is probably reflected in the relative temperature behaviour of characteristic lengths.Comment: Physica C (2012) in pres

Critical and non-critical coherence lengths in a two-band superconductor

We study the peculiarities of coherency in a two-gap superconductor. The both intraband couplings, inducing superconductivity in the independent bands, and interband pair-transfer interaction have been taken into account. On the basis of the Ginzburg-Landau equations derived from the Bogoliubov-de Gennes equations and the relevant self-consistency conditions for a two-gap system, we find critical and non-critical coherence lengths in the spatial behaviour of the fluctuations of order parameters. The character of the temperature dependencies of these length scales is determined by the relative contributions from intra- and interband interaction channels.Comment: Accepted for publication in Journal of Superconductivity and Novel Magnetis

Unusual boundary effect on coherency in two-band superconductors

We demonstrate that the healing of two-band superconductivity near the surface of the system is governed by length scales which are drastically different from correlation lengths. Similar to the one-band case, one of the characteristic lengths diverges at critical temperature $T_c$, while another one shows unusual behaviour having singularity at $T_{c+}<T_c$. By moving away from the boundary, these scales approach coherence lengths in the bulk state, where the divergence at $T_{c+}$ is removed by arbitrary weak interband coupling. Such a boundary-driven modification in coherency affects proximity phenomenon. We show that critical temperature of binary NS system can exhibit an inflection near $T_{c+}$ as two-band superconducting layer becomes thinner.Comment: 8 pages, 5 figure

Surface Effect on Spatial Length-Scales in a Two-Gap Superconductor

The healing of two-band superconductivity near its interface is studied. It is demonstrated that the restoration of superconductivity gaps in the immediate vicinity of the interface is governed by two length scales: the first one diverges at critical temperature T (c) , while the second one diverges at T (c+)&lt; T (c) . By moving away from the boundary, the temperature dependencies of characteristic lengths change so that singularity at T (c+) becomes removed in the bulk by arbitrary weak interband coupling. The asymptotes for the spatial behavior of gaps have been found analytically near the surface and approaching the bulk state.</p