Magnetic screening in proximity effect Josephson-junction arrays

The modulation with magnetic field of the sheet inductance measured on proximity effect Josephson-junction arrays (JJAs) is progressively vanishing on lowering the temperature, leading to a low temperature field-independent response. This behaviour is consistent with the decrease of the two-dimensional penetration length below the lattice parameter. Low temperature data are quantitatively compared with theoretical predictions based on the XY model in absence of thermal fluctuations. The results show that the description of a JJA within the XY model is incomplete and the system is put well beyond the weak screening limit which is usually assumed in order to invoke the well known frustrated XY model describing classical Josephson-junction arrays.Comment: 6 pages, 5 figure

Coherent transport in Josephson-Junction rhombi chain with quenched disorder

We consider a chain of Josephson-junction rhombi (proposed originally by Doucot and Vidal) in quantum regime. In a regular chain with no disorder in the maximally frustrated case when magnetic flux through each rhombi \Phi_r is equal to one half of superconductive flux quantum \Phi_0, Josephson current is due to correlated transport of pairs of Cooper pairs, i.e. charge is quantized in units of $4e$. Sufficiently strong deviation \delta\Phi =|\Phi_r-\Phi_0/2| > \delta\Phi^c from the maximally frustrated point brings the system back to usual $2e$-quantized supercurrent. For a regular chain \delta\Phi^c was calculated by us previously. Here we present detailed analysis of the effect of quenched disorder (random stray charges and random fluxes piercing rhombi) on the pairing effect.Comment: 21 pages, 5 figure

Observation of Ising-like critical fluctuations in frustrated Josephson junction arrays with modulated coupling energies

We report the results of ac sheet conductance measurements performed on fully frustrated square arrays of Josephson junctions whose coupling energy is periodically modulated in one of the principal lattice directions. Such systems are predicted to exhibit two distinct transitions: a low-temperature Ising-like transition triggered by the proliferation of domain walls and a high-temperature transition driven by the vortex unbinding mechanism of the Beresinskii-Kosterlitz-Thouless (BKT) theory. Both the superfluid and dissipative components of the conductance are found to exhibit features which unambiguously demonstrate the existence of a double transition whose properties are consistent with the Ising-BKT scenario.Comment: To be published in Physica C (Proceedings of the 2nd European Conference in School Format 'Vortex Matter in Superconductors'

Mapping the dynamic interactions between vortex species in highly anisotropic superconductors

Here we use highly sensitive magnetisation measurements performed using a Hall probe sensor on single crystals of highly anisotropic high temperature superconductors $Bi_{2}Sr_{2}CaCu_{2}O_{8}$ to study the dynamic interactions between the two species of vortices that exist in such superconductors. We observe a remarkable and clearly delineated high temperature regime that mirrors the underlying vortex phase diagram. Our results map out the parameter space over which these dynamic interaction processes can be used to create vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno

The Qur'an Seminar Commentary

The Qur'an Seminar Commentary is an unprecedented work of collaboration in the field of Qur'anic Studies, involving the insights of 25 scholars on 50 Qur'anic passages. These scholars represent a diverse range of disciplinary backgrounds and provide readers with unique insights into the latest trends of research in the Qur'an. This Commentary is a useful and illuminating reference work for students and scholars in the field of Qur'anic Studies