31 research outputs found
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 is small. Second,
for , a peak with a large energy gap 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
Current-induced highly dissipative domains in high Tc thin films
We have investigated the resistive response of high Tc thin films submitted
to a high density of current. For this purpose, current pulses were applied
into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the
time dependent voltage, we observe that at a certain critical current j*, a
highly dissipative domain develops somewhere along the bridge. The successive
formation of these domains produces stepped I-V characteristics. We present
evidences that these domains are not regions with a temperature above Tc, as
for hot spots. In fact this phenomenon appears to be analog to the nucleation
of phase-slip centers observed in conventional superconductors near Tc, but
here in contrast they appear in a wide temperature range. Under some
conditions, these domains will propagate and destroy the superconductivity
within the whole sample. We have measured the temperature dependence of j* and
found a similar behavior in the two investigated compounds. This temperature
dependence is just the one expected for the depairing current, but the
amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.
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.