6 research outputs found
Phase diagram and upper critical field of homogenously disordered epitaxial 3-dimensional NbN films
We report the evolution of superconducting properties with disorder, in
3-dimensional homogeneously disordered epitaxial NbN thin films. The effective
disorder in NbN is controlled from moderately clean limit down to Anderson
metal-insulator transition by changing the deposition conditions. We propose a
phase diagram for NbN in temperature-disorder plane. With increasing disorder
we observe that as kFl-->1 the superconducting transition temperature (Tc) and
minimum conductivity (sigma_0) go to zero. The phase diagram shows that in
homogeneously disordered 3-D NbN films, the metal-insulator transition and the
superconductor-insulator transition occur at a single quantum critical point at
kFl~1.Comment: To appear in Journal of Superconductivity and Novel Magnetism
(ICSM2010 proceedings
Multi-vortex versus interstitial vortices scenario in superconducting antidot arrays
In superconducting thin films, engineered lattice of antidots (holes) act as
an array of columnar pinning sites for the vortices and thus lead to vortex
matching phenomena at commensurate fields guided by the lattice spacing. The
strength and nature of vortex pinning is determined by the geometrical
characteristics of the antidot lattice (such as the lattice spacing ,
antidot diameter , lattice symmetry, orientation, etc) along with the
characteristic length scales of the superconducting thin films, viz., the
coherence length () and the penetration depth (). There are at
least two competing scenarios: (i) multiple vortices sit on each of the
antidots at a higher matching period, and, (ii) there is nucleation of vortices
at the interstitial sites at higher matching periods. Furthermore it is also
possible for the nucleated interstitial vortices to reorder under suitable
conditions. We present our experimental results on NbN antidot arrays in the
light of the above scenarios.Comment: Submitted to ISS2009 proceedings; references adde
Observation of Vortex Matching Phenomena in Antidot Array of NbN Thin Film
We report vortex matching phenomenon in rectangular antidot array fabricated
on epitaxial NbN thin film. The antidot array was fabricated using Focussed Ion
Beam milling technique. The magneto-transport measurements points to a period
doubling transition at higher magnetic field for rectangular lattices. The
results are discussed within the light of several models including the
multi-vortex model, the matched lattice model and the super-matched lattice
model.Comment: Added references, modified abstract and discussions and corrected
typo-graphic errors. Accepted for proceedings of M2S-IX 2009, Tokyo (Physica
C