Non linear flux flow in TiN superconducting thin film

We have studied the superconducting behavior of 100 nm Titanium Nitride (TiN) thin film in a perpendicular magnetic field. We found a zero field transition temperature of 4.6 K and a slope in the H-T plane of -0.745 T/K. At 4.2 K, we have performed careful transport measurements by measuring both the differential resistivity and voltage as a function of a DC current. Our results are analyzed in the framework of linear and non linear flux flow behavior. In particular, we have observed an electronic instability at high vortex velocities and from its dependence with respect to the applied magnetic field, we can exctract the inelastic scattering time and diffusion length of the quasiparticles

Low-lying excitations around a single vortex in a d-wave superconductor

A full quantum-mechanical treatment of the Bogoliubov-de Gennes equation for a single vortex in a d-wave superconductor is presented. First, we find low-energy states extended in four diagonal directions, which have no counterpart in a vortex of s-wave superconductors. The four-fold symmetry is due to 'quantum effect', which is enhanced when $p_{F}\xi$ is small. Second, for $p_{F}\xi \sim 1$, a peak with a large energy gap $E_{0}\sim \Delta$ is found in the density of states, which is due to the formation of the lowest bound states.Comment: 7pages, Revte

Strongly nonequilibrium flux flow in the presence of perforating submicron holes

We report on the effects of perforating submicron holes on the vortex dynamics of amorphous Nb0.7Ge0.3 microbridges in the strongly nonequilibrium mixed state, when vortex properties change substantially. In contrast to the weak nonequilibrium - when the presence of holes may result in either an increase (close to Tc) or a decrease (well below Tc) of the dissipation, in the strong nonequilibrium an enhanced dissipation is observed irrespectively of the bath temperature. Close to Tc this enhancement is similar to that in the weak nonequilibrium, but corresponds to vortices shrunk due to the Larkin-Ovchinnikov mechanism. At low temperatures the enhancement is a consequence of a weakening of the flux pinning by the holes in a regime where electron heating dominates the superconducting properties.Comment: 6 pages, 5 figure

Steps in the Negative-Differential-Conductivity Regime of a Superconductor

Current-voltage characteristics were measured in the mixed state of Y1Ba2Cu3O(7-delta) superconducting films in the regime where flux flow becomes unstable and the differential conductivity dj/dE becomes negative. Under conditions where its negative slope is steep, the j(E) curve develops a pronounced staircase like pattern. We attribute the steps in j(E) to the formation of a dynamical phase consisting of the succesive nucleation of quantized distortions in the local vortex velocity and flux distribution within the moving flux matter.Comment: 5 pages, 3 figure

Transport of magnetic vortices by surface acoustic waves

In a thin film of superconducting YBCO the impact of surface acoustic waves (SAWs) traveling on the piezoelectric substrate is investigated. A pronounced interaction between the ultrasonic waves and the vortex system in the type II superconductor is observed. The occurrence of a SAW-induced dc voltage perpendicular to the sound path is interpreted as {\em dynamic pinning} of vortices by the piezoacoustic SAW, which acts as a conveyor for the fluxquanta. Its antisymmetry with respect to the magnetic field directly evidences the induced, directed flux motion.This dynamic manipulation of vortices can be seen as an important step towards flux-based electronic devices.Comment: submitte

Thermal Conductivity of the Spin Peierls Compound CuGeO_3

The thermal conductivity of the Spin-Peierls (SP) compound CuGeO_3 was measured in magnetic fields up to 16 T. Above the SP transition, the heat transport due to spin excitations causes a peak at around 22 K, while below the transition the spin excitations rapidly diminish and the heat transport is dominated by phonons; however, the main scattering process of the phonons is with spin excitations, which demonstrates itself in an unusual peak in the thermal conductivity at about 5.5 K. This low-temperature peak is strongly suppressed with magnetic fields in excess of 12.5 T.Comment: 6 pages, including 2 postscript figure

Specific Heat of Zn-Doped YBa_{2}Cu_3O_{6.95}: Possible Evidence for Kondo Screening in the Superconducting State

The magnetic field dependence of the specific heat of Zn-doped single crystals of YBa_{2}Cu_3O_{6.95} was measured between 2 and 10 K and up to 8 Tesla. Doping levels of 0, 0.15%, 0.31%, and 1% were studied and compared. In particular we searched for the Schottky anomaly associated with the Zn-induced magnetic moments.Comment: 5 pages, 6 figure

Non-equilibrium Superconductivity and Quasiparticle Dynamics studied by Photo Induced Activation of Mm-Wave Absorption (PIAMA)

We present a study of non-equilibrium superconductivity in DyBa2Cu3O7-d using photo induced activation of mm-wave absorption (PIAMA). We monitor the time evolution of the thin film transmissivity at 5 cm-1 subject to pulsed infrared radiation. In addition to a positive bolometric signal we observe a second, faster, decay with a sign opposite to the bolometric signal for T>40 K. We attribute this to the unusual properties of quasi-particles residing near the nodes of an unconventional superconductor, resulting in a strong enhancement of the recombination time.Comment: 4 pages, REVTeX, Submitted to Phys. Rev. Letter

Normal-superconducting transition induced by high current densities in YBa2Cu3O7-d melt-textured samples and thin films: Similarities and differences

Current-voltage characteristics of top seeded melt-textured YBa2Cu3O7-d are presented. The samples were cut out of centimetric monoliths. Films characteristics were also measured on microbridges patterned on thin films grown by dc sputtering. For both types of samples, a quasi-discontinuity or quenching was observed for a current density J* several times the critical current density Jc. Though films and bulks much differ in their magnitude of both Jc and J*, a proposal is made as to a common intrinsic origin of the quenching phenomenon. The unique temperature dependence observed for the ratio J*/Jc, as well as the explanation of the pre-quenching regime in terms of a single dissipation model lend support to our proposal.Comment: 10 pages, 10 figures, submitted to Physical Review

Free flux flow resistivity in strongly overdoped high-T_c cuprate; purely viscous motion of the vortices in semiclassical d-wave superconductor

We report the free flux flow (FFF) resistivity associated with a purely viscous motion of the vortices in moderately clean d-wave superconductor Bi:2201 in the strongly overdoped regime (T_c=16K) for a wide range of the magnetic field in the vortex state. The FFF resistivity is obtained by measuring the microwave surface impedance at different microwave frequencies. It is found that the FFF resistivity is remarkably different from that of conventional s-wave superconductors. At low fields (H<0.2H_c2) the FFF resistivity increases linearly with H with a coefficient which is far larger than that found in conventional s-wave superconductors. At higher fields, the FFF resistivity increases in proportion to \sqrt H up to H_c2. Based on these results, the energy dissipation mechanism associated with the viscous vortex motion in "semiclassical" d-wave superconductors with gap nodes is discussed. Two possible scenarios are put forth for these field dependence; the enhancement of the quasiparticle relaxation rate and the reduction of the number of the quasiparticles participating the energy dissipation in d-wave vortex state.Comment: 9 pages 7 figures, to appear in Phys. Rev.