Major normal and superconducting parameters of high-Tc oxides

Effect of transport current on suppression of superconductivity with ultrashort laser pulse

We study the suppression of superconductivity with ultrashort laser pulse in the presence of transport current. The theoretical model is based on the Bardeen-Cooper-Schrieffer relations for the superconducting state coupled with kinetic equations for nonequilibrium Bogoliubov quasiparticles and phonons. The results of numerical simulation for picosecond and femtosecond laser pulses of optical and infrared ranges are given. We discuss the effects of main problem parameters, including the current density.

Isotope and multiband effects in layered superconductors

In this review we consider three classes of superconductors, namely cuprate superconductors, MgB(2) and the new Fe based superconductors. All of these three systems are layered materials and multiband compounds. Their pairing mechanisms are under discussion with the exception of MgB(2), which is widely accepted to be a 'conventional' electron-phonon interaction mediated superconductor, but extending the Bardeen-Cooper-Schrieffer (BCS) theory to account for multiband effects. Cuprates and Fe based superconductors have higher superconducting transition temperatures and more complex structures. Superconductivity is doping dependent in these material classes unlike in MgB(2) which, as a pure compound, has the highest values of T(c) and a rapid suppression of superconductivity with doping takes place. In all three material classes isotope effects have been observed, including exotic ones in the cuprates, and controversial ones in the Fe based materials. Before the area of high-temperature superconductivity, isotope effects on T(c) were the signature for phonon mediated superconductivity-even when deviations from the BCS value to smaller values were observed. Since the discovery of high T(c) materials this is no longer evident since competing mechanisms might exist and other mediating pairing interactions are discussed which are of purely electronic origin. In this work we will compare the three different material classes and especially discuss the experimentally observed isotope effects of all three systems and present a rather general analysis of them. Furthermore, we will concentrate on multiband signatures which are not generally accepted in cuprates even though they are manifest in various experiments, the evidence for those in MgB(2), and indications for them in the Fe based compounds. Mostly we will consider experimental data, but when possible also discuss theoretical models which are suited to explain the data.

Transport properties of the layered Rh oxide K0.49RhO2

We report measurements and analyses of resistivity, thermopower and the Hall coefficient of single-crystalline samples of the layered Rh oxide K(0.49)RhO(2). The resistivity is proportional to the square of the temperature up to 300 K, and the thermopower is proportional to the temperature up to 140 K. The Hall coefficient increases linearly with the temperature above 100 K, which is ascribed to the triangular network of Rh in this compound. The different transport properties between Na(x)CoO(2) and K(0.49)RhO(2) are discussed on the basis of the different bandwidth between Co and Rh evaluated from the magnetotransport.

Magnetic imaging of pearl vortices in artificially layered (Ba0.9Nd0.1CuO2+x)m/(CaCuO2)n systems

We have used scanning SQUID magnetometry to image vortices in ultrathin (Ba0.9Nd0.1CuO2+x)(m)/(CaCuO2)(n) high temperature superconductor samples, with as few as three superconducting CuO2 planes. The Pearl lengths (Lambda=2lambda(2)(L)/d, lambda(L) the London penetration depth, d the superconducting film thickness) in these samples, as determined by fits to the vortex images, agree with those by local susceptibility measurements, and can be as long as 1 mm. The in-plane penetration depths lambda(ab) inferred from the Pearl lengths are longer than many bulk cuprates with comparable critical temperatures. We speculate on the causes of the long penetration depths, and on the possibility of exploiting the unique properties of these superconductors for basic experiments.

Mixed state of a dirty two-band superconductor: application to MgB2

We investigate the vortex state in a two-band superconductor with strong intraband and weak interband electronic scattering rates. Coupled Usadel equations are solved numerically, and the distributions of the pair potentials and local densities of states are calculated for two bands at different values of magnetic fields. The existence of two distinct length scales corresponding to different bands is demonstrated. The results provide qualitative interpretation of recent scanning tunneling microscopy experiments on vortex structure imaging in MgB2.