A two-coil mutual inductance technique to study matching effect in disordered NbN thin films

Although matching effects in superconducting anti-dot arrays have been studied extensively through magneto-resistance oscillations, these investigations have been restricted to a very narrow temperature window close to the superconducting transition. Here we report a "two coil" mutual inductance technique, which allows the study of this phenomenon deep in the superconducting state, through a direct measurement of the magnetic field variation of the shielding response. We demonstrate how this technique can be used to resolve outstanding issues on the origin of matching effects in superconducting thin films with periodic array of holes grown on anodized alumina membranes

Origin of Matching Effect in Anti-dot Array of Superconducting NbN Thin Films

We investigate the origin of matching effect observed in disordered superconducting NbN thin films with periodic array of holes. In addition to the periodic variation in the electrical resistance just above the superconducting transition temperature, Tc0, we find pronounced periodic variations with magnetic field in all dynamical quantities which can be influenced by flux-line motion under an external drive such as the magnetic shielding response and the critical current which survive in some samples down to temperatures as low as 0.09Tc0. In contrast, the superconducting energy gap, D which is a true thermodynamic quantity does not show any periodic variation with magnetic fields for the same films. Our results show that commensurate pinning of the flux line lattice driven by vortex-vortex interaction is the dominant mechanism for the observed matching effects in these superconducting anti-dot films rather than Little-Parks like quantum interference effect.Comment: 18 pages, 6 figure

INTRODUCTION OF A TEST BATTERY FOR IDENTIFICATION OF TALENT IN FEMALE VOLLEYBALL PLAYERS

Purpose: To develop a standardized test battery for the selection and identification of talented female volleyball players. Methods: Two hundred (N=200) junior national level female volleyball players (Mage=15.5 years & SDage=± 1.0) from five states in India have voluntarily participated in this study. Total 22 test items comprise of eight anthropometric measurements, eight physical fitness and six volleyball skills were administered on the subject according to standard procedure. Results: After administering item analysis, residual correlation matrix, and factor analysis eight test items i.e. weight, height, vertical jump, spiking, setting, service, service reception & passing and blocking were finally elicited to constitute the test battery for identification of talent in female volleyball players. The reliability coefficient using split-half was 0.82 and for validity index item-sum correlation coefficients were 0.73 to 0.79 (

Size induced metal insulator transition in nanostructured Niobium thin films: Intragranular and intergranular contributions

With a reduction in the average grain size in nanostructured films of elemental Nb, we observe a systematic crossover from metallic to weakly-insulating behavior. An analysis of the temperature dependence of the resistivity in the insulating phase clearly indicates the existence of two distinct activation energies corresponding to inter-granular and intra-granular mechanisms of transport. While the high temperature behavior is dominated by grain boundary scattering of the conduction electrons, the effect of discretization of energy levels due to quantum confinement shows up at low temperatures. We show that the energy barrier at the grain boundary is proportional to the width of the largely disordered inter-granular region, which increases with a decrease in the grain size. For a metal-insulator transition to occur in nano-Nb due to the opening up of an energy gap at the grain boundary, the critical grain size is ~ 8nm and the corresponding grain boundary width is ~ 1.1nm

Upper critical field in nanostructured Nb: Competing effects of the reduction in density of states and the mean free path

We show that the upper critical field in nanometer-sized Nb particles is governed by the changes in the effective Ginzburg-Landau coherence length occurring due to two competing factors: (i) the decrease in the grain size and consequent increase of disorder, and (ii) the effective decrease in the density of states at the Fermi level due to the formation of a Kubo gap. As a result, the upper critical field (HC2) and irreversibility fields (Hirr) in nanostructured Nb show non-monotonic grain size dependences. Between 60nm to 20nm, HC2 is found to increase by 2.5times while there is no appreciable decrease in the superconducting transition temperature (TC) from its bulk value of 9.4K. This can be ascribed to a decrease in the coherence length due to a reduction in the mean free path with decreasing size. Below 20 nm, however, HC2 decreases with decreasing size. In this size range (<20 nm), there also occurs a decrease in the TC as well as the superconducting energy gap. The decrease in HC2 in this regime can be ascribed to the decrease in the density of states at the Fermi level due to a quantization in the electronic energy levels