Effects of Electron-Electron and Electron-Phonon Interactions in Weakly Disordered Conductors and Heterostuctures

We investigate quantum corrections to the conductivity due to the interference of electron-electron (electron-phonon) scattering and elastic electron scattering in weakly disordered conductors. The electron-electron interaction results in a negative $T^2 \ln T$-correction in a 3D conductor. In a quasi-two-dimensional conductor, $d < v_F/T$ ($d$ is the thickness, $v_F$ is the Fermi velocity), with 3D electron spectrum this correction is linear in temperature and differs from that for 2D electrons (G. Zala et. al., Phys. Rev.B {\bf 64}, 214204 (2001)) by a numerical factor. In a quasi-one-dimensional conductor, temperature-dependent correction is proportional to $T^2$. The electron interaction via exchange of virtual phonons also gives $T^2$-correction. The contribution of thermal phonons interacting with electrons via the screened deformation potential results in $T^4$-term and via unscreened deformation potential results in $T^2$-term. The interference contributions dominate over pure electron-phonon scattering in a wide temperature range, which extends with increasing disorder.Comment: 6 pages, 2figure

Current-induced critical state in NbN thin-film structures

The temperature dependence of the critical current of NbN thin-film bridges was experimentally studied. At low temperatures we observed significant enhancement (up to two times at 4 K) of the critical current density over de-pinning value in the sub-micrometer wide bridges. This enhancement can be described by an increase of the edge barrier for penetration of magnetic vortices into narrow superconducting strips

Ultra-thin TaN films for superconducting nanowire single-photon detectors

Ultra-thin films of superconducting tantalum nitride are deposited by reactive magnetron sputtering on heated sapphire substrates. The critical temperature T C=10.25 K is reached for films thicker than 10 nm. A superconducting nanowire single-photon detector in the form of a meander line with a width of 110 nm was made from 5 nm thick TaN film. The detector had a transition temperature of 8.3 K and a critical current density of 4 MA/cm2 at 4.2 K. A photon detection efficiency of 20% has been obtained for the detector with a filling factor of 0.55 at wavelengths up to 700 nm