541 research outputs found

    Superconductor-Insulator Transitions and Insulators with Localized Pairs

    Full text link
    Two experiments are described which are related to the problem of localized Cooper pairs. Magnetic-field-tuned superconductor-insulator transition was studied in amorphous In--O films with onset of the superconducting transition in zero field near 2 K. Experiments performed in the temperature range T>0.3 K indicate that at the critical field, B=B_c, the first derivative of the resistance dR/dT is non-zero at T=0 and hence the scaling relations should be written in more general form. Study of the magnetotransport of high-resistance metastable alloy Cd-Sb on the insulating side of the superconductor-insulator transition revealed below 0.1 K a shunting condiction mechanism in addition to usual one-particle hopping. Possibility of pair hopping is discussed.Comment: 4 pages, 5 PS figures, uses psfig.sty; contribution to the Conference MESO-97, June 1997, Chernogolovka, Russi

    Localized - delocalized electron quantum phase transitions

    Full text link
    Metal--insulator transitions and transitions between different quantum Hall liquids are used to describe the physical ideas forming the basis of quantum phase transitions and the methods of application of theoretical results in processing experimental data. The following two theoretical schemes are discussed and compared: the general theory of quantum phase transitions, which has been developed according to the theory of thermodynamic phase transitions and relies on the concept of a partition function, and a theory which is based on a scaling hypothesis and the renormalization-group concept borrowed from quantum electrodynamics, with the results formulated in terms of flow diagrams.Comment: 27 pages, 20 figure

    Width of the Zero-Field Superconducting Resistive Transition in the Vicinity of the Localization Threshold

    Full text link
    Resistive superconducting zero-field transition in amorphous In-O films in states from the vicinity of the insulator-superconductor transition is analyzed in terms of two characteristic temperatures: the upper one, Tc0T_{c0}, where the finite amplitude of the order parameter is established and the lower one, TcT_c, where the phase ordering takes place. It follows from the magnetoresistance measurements that the resistance in between, Tc<T<Tc0T_c<T<T_{c0}, cannot be ascribed to dissipation by thermally dissociated vortex pairs. So, it is not Kosterlitz-Thouless-Berezinskii transition that happens at TcT_c.Comment: 4 pages, 3 figure

    Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition

    Get PDF
    We investigate ultrathin superconducting TiN films, which are very close to the localization threshold. Perpendicular magnetic field drives the films from the superconducting to an insulating state, with very high resistance. Further increase of the magnetic field leads to an exponential decay of the resistance towards a finite value. In the limit of low temperatures, the saturation value can be very accurately extrapolated to the universal quantum resistance h/e^2. Our analysis suggests that at high magnetic fields a new ground state, distinct from the normal metallic state occurring above the superconducting transition temperature, is formed. A comparison with other studies on different materials indicates that the quantum metallic phase following the magnetic-field-induced insulating phase is a generic property of systems close to the disorder-driven superconductor-insulator transition.Comment: 4 pages, 4 figures, published versio

    Superconductor insulator transition in thin films driven by an orbital parallel magnetic field effect

    Full text link
    We study theoretically orbital effects of a parallel magnetic field applied to a disordered superconducting film. We find that the field reduces the phase stiffness and leads to strong quantum phase fluctuations driving the system into an insulating behavior. This microscopic model shows that the critical field decreases with the sheet resistance, in agreement with recent experimental results. The predictions of this model can be used to discriminate spin and orbital effects. We find that experiments conducted by A. Johansson \textit{et al.} are more consistent with the orbital mechanism.Comment: 4 pages, 2 figure

    Influence of chemical pressure effects on nonlinear thermal conductivity of intrinsically granular superconductors

    Full text link
    Using a 2D model of capacitively coupled Josephson junction arrays (created by a network of twin boundary dislocations with strain fields acting as an insulating barrier between hole-rich domains in underdoped crystals), we study the influence of chemical pressure on nonlinear thermal conductivity (NLTC) of an intrinsically granular superconductor. Quite a substantial enhancement of NLTC is predicted when intrinsic chemoelectric field closely matches the externally produced thermoelectric field. The estimates of the model parameters suggest a realistic possibility to experimentally monitor this effect in non-stoichiometric superconductors.Comment: 10 pages, 2 figure

    Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films

    Full text link
    We study the response of a thin superconducting amorphous InO film with variable oxygen content to a parallel magnetic field. A field-induced superconductor-insulator transition (SIT) is observed that is very similar to the one in normal magnetic fields. As the boson-vortex duality, which is the key-stone of the theory of the field-induced SIT, is obviously absent in the parallel configuration, we have to draw conclusion about the theory insufficiency.Comment: 3 pages, 4 figure
    • …
    corecore