Effect of disorder in MgB2 thin films

We report on scanning tunneling spectroscopy studies of magnesium diboride (MgB2) thin films grown by different techniques. The films have critical temperatures ranging between 28 and 41 K with very different upper critical fields. We find that the superconducting gap associated with the sigma band decreases almost linearly with decreasing critical temperature while the gap associated with the pi band is only very weakly affected in the range of critical temperatures above 30 K. In the sample with the lowest critical temperature (28 K) we observe a small increase of the pi gap that can only be explained in terms of an increase in the interband scattering. The tunneling data was analyzed in the framework of the two-band model. The magnetic-field-dependent tunneling spectra and the upper critical field measurements of these disordered samples can be consistently explained in terms of an increase of disorder that mostly affects the pi band in samples with reduced critical temperatures

Oxidation Kinetics in SrTiO₃ Homoepitaxy

ABSTRACTUsing an oblique-incidence optical reflectivity difference technique, we investigated kinetic processes in SrTiO3 homoepitaxy on SrTiO3(001) under pulsed laser deposition conditions. Depending upon growth temperature and oxygen ambient pressure, we found that the oxidation of an as-grown SrTiO3 monolayer may take a much longer time to complete than the recrystallization of the monolayer. The oxidation reaction was found to be characterized by an effective activation energy barrier of 1.35 eV and a large pre-exponential factor.</jats:p

Misfit relaxation in SrTiO₃/SrRuO₃ bilayer films on LaA1O₃(100) substrates

Besides perfect dislocations, partial dislocations were proposed as effective means for misfit relaxation in the heretostructure system [1]. The microstructure of SrRuO3 films on SrTiO3 and LaA1O3 substrates have been studied. While misfit dislocations could be hardly found at the SrTiO3/SrRuO3 interface [2], high density of defects was observed in the SrRuO3/LaA1O3 interfaces [3]. in this paper, we report the high-resolution electron microscopy study of the SrTiO3/SrRuO3 bilayer films on (100) LaA1O3 substrates. The emphasis is focused on the means of misfit relaxation at the two interfaces.Figure 1(a) is a low magnification cross-sectional image of a two-layer SrTiO3/SrRuO3 film on LaA1O3 taken along the [110] direction of the substrate. A high density of defects were observed along the SrRuO3/LaA1O3 interface. Figure 1(b) is a quarter of a superposed electron diffraction pattern (EDP) from the SrTiO3/SrRuO3 interface area, while fig. 1(c) is from the SrRuO3/LaA1O3 interface area.</jats:p