59 research outputs found
Strong thermal fluctuations in cuprate superconductors in magnetic field above Tc
Recent measurements of fluctuation diamagnetism in high temperature
superconductors show distinct features above and below Tc, which can not be
explained by simple gaussian fluctuation theory. Self consistent calculation of
magnetization in layered high temperature superconductors, based on the
Ginzburg-Landau-Lawrence-Doniach model and including all Landau levels is
presented. The results agree well with the experimental data in wide region
around Tc, including both the vortex liquid below Tc and the normal state above
Tc. The gaussian fluctuation theory significantly over estimates the
diamagnetism for strong fluctuations. It is demonstrated that the intersection
point of magnetization curves appears in the region where the lowest Landau
level contribution dominates.Comment: 5 pages, 4 figure
Effect of the type I to type II Weyl semimetal topological transition on superconductivity
The influence of recently discovered topological transition between type I
and type II Weyl semi-metals on superconductivity is considered. A set of
Gorkov equations for weak superconductivity in Weyl semi-metal under
topological phase transition is derived and solved. The critical temperature
and superconducting gap both have spike in the point the transition point as
function of the tilt parameter of the Dirac cone determined in turn by the
material parameters like pressure. The spectrum of superconducting excitations
is different in two phases: the sharp cone pinnacle is characteristic for a
type I, while two parallel almost flat bands, are formed in type II. Spectral
density is calculated on both sides of transition demonstrate different weight
of the bands. The superconductivity thus can be used as a clear indicator for
the topological transformation. Results are discussed in the light of recent
experiments.Comment: 13 pages, 5 figure
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