7 research outputs found
On the superconductivity in the system with preformed pairs
We discuss the phenomenology of the superconductivity resulting from the bose
condensation of the preformed pairs coexisting with unpaired fermions. We show
that this transition is more mean field like than usual bose condensation, i.e.
it is characterized by a relatively small value of the Ginzburg parameter. We
consider the Hall effect in the vortex flow regime and in the fluctuational
regime above and show that in this situation it is much less than in the
transition driven entirely by bose condesation but much larger than in a usual
superconductivity. We analyse the available Hall data and conclude that this
phenomenology describes reasonably well the data in the underdoped materials of
family but is not an appropriate description of optimally doped
materials or underdoped .Comment: Latex/Revtex file, 2 Postscript figures, 10 page
Pseudogap in a thin film of a conventional superconductor
A superconducting state is characterized by the gap in the electronic density
of states which vanishes at the superconducting transition temperature Tc. It
was discovered that in high temperature superconductors a noticeable depression
in the density of states still remains even at temperatures above Tc; this
feature being called pseudogap. Here we show that a pseudogap exists in a
conventional superconductor: ultrathin titanium nitride films over a wide range
of temperatures above Tc. Our study reveals that this pseudogap state is
induced by superconducting fluctuations and favored by two-dimensionality and
by the proximity to the transition to the insulating state. A general character
of the observed phenomenon provides a powerful tool to discriminate between
fluctuations as the origin of the pseudogap state, and other contributions in
the layered high temperature superconductor compounds.Comment: 26 pages, 4 figure
Modification by high pressure of fluctuation paraconductivity of underdoped HoBa2Cu3O7-δ single crystals
Superconducting phase transitions in ultrathin TiN films
We investigate transition to the superconducting state in the ultrathin
titanium nitride films on approach to superconductor-insulator transition.
Building on the complete account of quantum contributions to conductivity, we
demonstrate that the resistance of thin superconducting films exhibits a
non-monotonic temperature behaviour due to the competition between weak
localization, electron-electron interaction, and superconducting fluctuations.
We show that superconducting fluctuations give rise to an appreciable decrease
in the resistance even at temperatures well exceeding the superconducting
transition temperature, T_c, with this decrease being dominated by the
Maki-Thompson process.The transition to a global phase-coherent superconducting
state occurs via the Berezinskii-Kosterlitz-Thouless (BKT) transition, which we
observe both by power-law behaviour in current-voltage characteristics and by
flux flow transport in the magnetic field. The ratio T_{BKT}/T_c follows the
universal Beasley-Mooij-Orlando relation. Our results call for revisiting the
past data on superconducting transition in thin disordered films.Comment: 6 pages, 4 figure