9 research outputs found
Proximity effect and strong coupling superconductivity in nanostructures built with an STM
We present high resolution tunneling spectroscopy data at very low
temperatures on superconducting nanostructures of lead built with an STM. By
applying magnetic fields, superconductivity is restricted to length scales of
the order of the coherence length. We measure the tunneling conductance and
analyze the phonon structure and the low energy DOS. We demonstrate the
influence of the geometry of the system on the magnetic field dependence of the
tunneling density of states, which is gapless in a large range of fields. The
behavior of the features in the tunneling conductance associated to phonon
modes are explained within current models.Comment: 4 figures, 4 page
A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum
Varying the angle Theta between applied field and the conducting planes of a
layered superconductor in a small interval close to the plane-parallel field
direction, a large number of superconducting states with unusual properties may
be produced. For these states, the pair breaking effect of the magnetic field
affects both the orbital and the spin degree of freedom. This leads to pair
wave functions with finite momentum, which are labeled by Landau quantum
numbers 0<n<\infty. The stable order parameter structure and magnetic field
distribution for these states is found by minimizing the quasiclassical free
energy near H_{c2} including nonlinear terms. One finds states with coexisting
line-like and point-like order parameter zeros and states with coexisting
vortices and antivortices. The magnetic response may be diamagnetic or
paramagnetic depending on the position within the unit cell. The structure of
the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered.
The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is
analyzed and the physical reason for the occupation of higher Landau levels is
pointed out.Comment: 24 pages, 11 figure
Unconventional vortex dynamics in mesoscopic superconducting corbino disks
The discrete shell structure of vortex matter strongly influences the flux
dynamics in mesoscopic superconducting Corbino disks. While the dynamical
behavior is well understood in large and in very small disks, in the
intermediate-size regime it occurs to be much more complex and unusual, due to
(in)commensurability between the vortex shells. We demonstrate unconventional
vortex dynamics (inversion of shell velocities with respect to the gradient
driving force) and angular melting (propagating from the boundary where the
shear stress is minimum, towards the center) in mesoscopic Corbino disks.Comment: 4 pages, 3 figure
Static and dynamic behaviours of multivortex states in a superconducting sample with mesoscopic pinning sites
This preliminary work has focused on the static
transitions between the multivortex states interacting with square
arrays of the mesoscopic pinning sites in superconducting samples.
Our results were obtained from an extensive series of numerical
simulations as functions of the magnetic field, pinning radius,
and sample size. We have presented a wide range of multivortex
configurations from commensurate dimer states to more concentric
vortex shells at the matching fields. The stability of these
states was also studied by means of the current-voltage V(I)
curves which illustrate dynamic phase transitions as a function of
applied driving force. These transitions manifested themselves as
either a sudden jump in velocity or a nonlinear increase with
velocity fluctuations in V(I) curves. We have investigated
whether that the phase transitions between the pinned regime and
the elastic flow regime are indicative of the stability of the
initial vortex states. The variety of intermediate flow phases is
attributed to large pinning size (reentrant behavior), strong
commensurability and caging effects. In particular, three-shell
vortex structures were obtained in the presence of larger pinning
sites at adequate matching magnetic fields