arXiv subjects
Publications and source records attributed to J. Kolacek.
A boundary condition for the Ginzburg-Landau wave function at surfaces biased by a strong electric field is derived within the de Gennes approach. This condition provides a simple theory of the field effect on the critical temperature of superconducting layers.
The electrostatic potential close to the surface of superconductors in the Meissner state is discussed. We show that beside the Bernoulli potential, the quasiparticle screening, and the thermodynamic contribution due to Rickayzen, there is a non-local contribution which is large for both type-I and weak type-II superconductors.
The Budd-Vannimenus theorem is modified to apply to superconductors in the Meissner state. The obtained identity links the surface value of the electrostatic potential to the density of free energy at the surface which allows one to evaluate the electrostatic potential observed via the capacitive pickup without the explicit solution of the charge profile.
Temperature dependence of far-infrared transmission of NbN thin films deposited on MgO and Si substrates was measured at several frequencies from 0.4 up to 4.3 THz. Exponential increase of relative penetration depth at low temperatures and a peak in transmission near Tc was observed for frequencies below the optical gap. On the contrary, transmission measured at frequencies above the gap exhibits only flat, almost linear temperature dependence. This behavior is consistent with the BCS theory of superconductivity. Similar measurements were performed also on YBaCuO thin films deposited on MgO and sapphire substrates. Low-temperature variation of transmission is linear or constant and the peak below Tc predicted by the BCS theory is not observed. Flat temperature dependence at higher frequencies indicates that the photon energy was sufficient for excitation over the optical gap. The s-wave BCS theory is adequate for NbN films but not for the YBCO materials.
The electric charge density in the vortex lattice of superconductors is studied within the Ginzburg-Landau theory. We show that the electrostatic potential $ϕ$ is proportional to the GL function, $ϕ\propto|ψ|^2-|ψ_\infty|^2$. Numerical results for the triangular vortex lattice are presented.
The electric charge density in mesoscopic superconductors with circular symmetry, i.e. disks and cylinders, is studied within the phenomenological Ginzburg-Landau approach. We found that even in the Meissner state there is a charge redistribution in the sample which makes the sample edge become negatively charged. In the vortex state there is a competition between this Meissner charge and the vortex charge which may change the polarity of the charge at the sample edge with increasing magnetic field. It is shown analytically that in spite of the charge redistribution the mesoscopic sample as a whole remains electrically neutral.
The Hall voltage sign reversal is consistently explained by the model in which vortices with the superconducting and normal state charge carriers are regarded as three subsystems mutually connected by interactions. The equations of motion for these three subsystems are solved simultaneously and a new formula for the Hall resistivity is obtained. It is shown that it is possible to explain qualitatively experimental data by this model.
Generally it is accepted that electric field E in type II superconductors is created by the vortex motion, so that it is proportional to the vortex velocity v_L. This assertion is based on the Josephson relation E = - v_L x B, which was derived and is valid if no transport current is present. We present arguments showing that if transport current is present, static electric field is proportional to the relative velocity of vortices in respect to the velocity of superconducting fluid v_s, so that in this case generalised Josephson relation E = v_s - v_L x B is valid.
Measurements of the far infrared magnetotransmission of YBa2(ZnxCu(1-x))3O(7-d) thin film (x = 0.025) deposited on a wedged MgO substrate are reported. The application of magnetic field perpendicular to the ab plane produces at low temperature a linear increase of transmission for frequencies below 30 cm-1. We present a model of high frequency vortex dynamics which qualitatively explains these results.
The vortex lattice with the superconducting and normal state charge carriers fractions may be regarded as three independent subsystems mutually connected by interactions. The equation of motion for these three subsystems must be solved simultaneously. In this way a new consistent theory of the vortex dynamics is obtained and the magnetoconductivity calculated.
We have found that Fermi contours of a two-dimensional electron gas at $\rmGaAs/Al_xGa_{1-x}As$ interface deviate from a standard circular shape under the combined influence of an approximately triangular confining potential and the strong in-plane magnetic field. The distortion of a Fermi contour manifests itself through an increase of the electron effective cyclotron mass which has been measured by the cyclotron resonance in the far-infrared transmission spectra and by the thermal damping of Shubnikov-de Haas oscillations in tilted magnetic fields with an in-plane component up to 5 T. The observed increase of the cyclotron effective mass reaches almost 5 \% of its zero field value which is in good agreement with results of a self-consistent calculation.