1,194 research outputs found
Instabilities of the normal state in current-biased narrow superconducting strips
We study the current-voltage characteristic of narrow superconducting strips in the gapless regime near the critical temperature in the framework of the Ginzburg-Landau model. Our focus is on its instabilities occurring at high current biases. The latter are consequences of dynamical states with periodic phase-slip events in space and time. We analyze their structure and derive the value of the reentrance current at the onset of the instability of the normal state. It is expressed in terms of the kinetic coefficient of the time-dependent Ginzburg-Landau equation and calculated numerically
Quantum Fluctuations and Dynamic Clustering of Fluctuating Cooper Pairs
We derive exact expressions for the fluctuation conductivity in two
dimensional superconductors as a function of temperature and magnetic field in
the whole fluctuation region above the upper critical field H_{c2}(T). Focusing
on the vicinity of the quantum phase transition near zero temperature, we
propose that as the magnetic field approaches the line near H_{c2}(0) from
above, a peculiar dynamic state consisting of clusters of coherently rotating
fluctuation Cooper-pairs forms and estimate the characteristic size and
lifetime of such clusters. We find the zero temperature magnetic field
dependence of the the transverse magnetoconductivity above H_{c2}(0) in layered
superconductors.Comment: 5 pages, 3 figure
Electron Transport Properties of Composite Ferroelectrics
We study electron transport in composite ferroelectrics --- materials
consisting of metallic grains embedded in a ferroelectric matrix. Due to its
complex tunable morphology the thermodynamic properties of these materials can
be essentially different from bulk or thin-film ferroelectrics. We calculate
the conductivity of composite ferroelectrics by taking into account the
interplay between charge localization, multiple grain boundaries, strong
Coulomb repulsion, and ferroelectric order parameter. We show that the
ferroelectricity plays a crucial role on the temperature behavior of the
conductivity in the vicinity of the ferroelectric-paraelectric transition.Comment: 6 pages, 3 figure
Giant Magnetoresistance in Nanogranular Magnets
We study the giant magnetoresistance of nanogranular magnets in the presence
of an external magnetic field and finite temperature. We show that the
magnetization of arrays of nanogranular magnets has hysteretic behaviour at low
temperatures leading to a double peak in the magnetoresistance which coalesces
at high temperatures into a single peak. We numerically calculate the
magnetization of magnetic domains and the motion of domain walls in this system
using a combined mean-field approach and a model for an elastic membrane moving
in a random medium, respectively. From the obtained results, we calculate the
electric resistivity as a function of magnetic field and temperature. Our
findings show excellent agreement with various experimental data.Comment: 4 pages, 3 figure
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