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Experimental results indicating a direct disorder-induced superconductor–insulator transition in NbTiN thin films have been reported. It has been shown that an increase in the resistance per square in the normal state is accompanied by the suppression of the critical temperature of the superconducting transition according to the fermion mechanism of suppression of superconductivity by disorder. At the same time, the temperature of the Berezinskii–Kosterlitz–Thouless transition is completely suppressed at a nonzero critical temperature and, then, the ground state changes to insulating, which is characteristic of the boson model of suppression of superconductivity by disorder. It has been shown that the temperature dependences of the resistance of insulating films follow the Arrhenius activation law. [ABSTRACT FROM AUTHOR]

We demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structure in the ferromagnetic layers results in directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity of up to three orders of magnitude can be achieved with spatial critical temperature modulation of 5% of Tc. The effect could be exploited in low temperature nonvolatile logic and storage elements. [ABSTRACT FROM AUTHOR]

A method to treat the surface of Nb is described, which potentially can improve the performance of superconducting rf cavities. We present tunneling and x-ray photoemission spectroscopy measurements at the surface of cavity-grade niobium samples coated with a 3 nm alumina overlayer deposited by atomic layer deposition. The coated samples baked in ultrahigh vacuum at low temperature degraded superconducting surface. However, at temperatures above 450 C, the tunneling conductance curves show significant improvements in the superconducting density of states compared with untreated surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Among the different methods of vortex study in superconductors, Scanning Tunneling Microscopy (STM) and Spectroscopy (STS), occupies a particular place. Due to its extraordinary spatial and energy resolution STS allows the study of vortices in real space on a nanometeric scale. In practice however, the success of the observation of vortices by STS depends strongly on the surface quality. Usually highly uniform surfaces are needed to distinguish vortices. As a result of this limitation, the vortex lattice has been successfully studied only in a limited number of superconductors. Here we suggest a simple method extending the vortex analysis to ‘difficult cases’ of ‘bad’ superconductors, thin films and even granular materials. In this method the STM tip is positioned in a chosen location of the sample and the local tunneling spectroscopy is continuously performed while the magnetic field is slowly swept. The vortices entering the sample move under the tip and are detected due to the change in the shape of tunneling spectra. We show that the method allows not only to follow the vortex penetration but also to estimate essential superconducting parameters such as the penetration and the coherence lengths. Moreover, it authorizes the study of the vortex cores in the cases where scanning is difficult or impossible. [Copyright &y& Elsevier]