arXiv subjects

I. L. Landau

Publications and source records attributed to I. L. Landau.

23 records · Page 2Linked to original sources

arXiv2002

Some remarks on vortex matter in high temperature superconductors

We show that some experimentally observed features of vortex matter in high temperature superconductors may be interpreted in simpler ways than it is usually done. In particular, we consider magnetic flux creep at low temperatures as well as the irreversibility line in the H-T phase diagram. We also discuss a new approach to the analysis of the equilibrium magnetization in the mixed state of type-II superconductors and we suggest an alternative configuration for the mixed state in magnetic fields close to the upper critical field.

cond-mat.supr-con↗

arXiv2002

Temperature dependence of the upper critical field of type-II superconductors from isothermal magnetization data. Application to high temperature superconductors

Using the Ginzburg-Landau theory in very general terms, we develop a simple scaling procedure which allows to establish the temperature dependence of the upper critical field and the value of the superconducting critical temperature Tc of type-II superconductors from measurements of the reversible isothermal magnetization. An analysis of existing experimental data shows that the normalized dependencies the upper critical field on T/Tc are practically identical for all families of high temperature superconductors at all temperatures for which the magnetization data are available.

cond-mat.supr-con↗

arXiv2002

Model of the mixed state of type-II superconductors in high magnetic fields

In superconductors with large values of the Ginzburg-Landau parameter, exposed to magnetic fields close to the upper critical field, the magnetic field is practically homogeneous across the sample and the density of supercurrents is negligibly small. In this case, there is no obvious reason for the formation of Abrikosov vortices, characteristic for the commonly known mixed state. We consider an alternative model for describing the mixed state. We argue that with decreasing magnetic field the traditional vortex structure is adopted via a first order phase transition, revealed by discontinuities in the magnetization as well as the resistivity.

cond-mat.supr-con↗

arXiv2001

On the vortex motion in high temperature superconductors

We show that prominent features in voltage-current characteristics, recently measured in the mixed state of high-Tc superconductors and interpreted as evidence for an irreversibility line or a vortex-glass transition, may very well be explained with the simplest Kim-Anderson approach describing the vortex motion. In this case, the irreversibility line is not related to a transition in the system of vortices. Consulting numerous experimental reports on this subject we have not found a single example, which is in contradiction with this view.

cond-mat.supr-con↗

arXiv2000

Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments

We present an experimental study of thermally activated flux creep in a superconducting ring-shaped epitaxial YBCO film as well as a new way of analyzing the experimental data. The measurements were made in a wide range of temperatures between 10 and 83 K. The upper temperature limit was dictated by our experimental technique and at low temperatures we were limited by a crossover to quantum tunneling of vortices. It is shown that the experimental data can very well be described by assuming a simple thermally activated hopping of vortices or vortex bundles over potential barriers, whereby the hopping flux objects remain the same for all currents and temperatures. The new procedure of data analysis also allows to establish the current and temperature dependencies of the flux-creep activation energy U, as well as the temperature dependence of the critical current Ic, from the flux-creep rates measured at different temperatures. The variation of the activation energy with current, U(I/Ic), is then used to reconstruct the profile of the potential barriers in real space.

cond-mat.supr-con↗