284 research outputs found
Superconductor-insulator duality for the array of Josephson wires
We propose novel model system for the studies of superconductor-insulator
transitions, which is a regular lattice, whose each link consists of
Josephson-junction chain of junctions in sequence. The theory of such
an array is developed for the case of semiclassical junctions with the
Josephson energy large compared to the junctions's Coulomb energy .
Exact duality transformation is derived, which transforms the Hamiltonian of
the proposed model into a standard Hamiltonian of JJ array. The nature of the
ground state is controlled (in the absence of random offset charges) by the
parameter , with superconductive state
corresponding to small . The values of are calculated for
magnetic frustrations and . Temperature of superconductive
transition and is estimated for the same values of . In
presence of strong random offset charges, the T=0 phase diagram is controlled
by the parameter ; we estimated critical value
.Comment: 5 pages, 2 figure
Theory of 4e versus 2e supercurrent in frustrated Josepshon-junction rhombi chain
We consider a chain of Josepshon-junction rhombi (proposed originally in
\cite{Doucot}) in quantum regime, and in the realistic case when charging
effects are determined by junction capacitances. In the maximally frustrated
case when magnetic flux through each rhombi is equal to one half of
superconductive flux quantum , Josepshon current is due to correlated
transport of {\em pairs of Cooper pairs}, i.e. charge is quantized in units of
. Sufficiently strong deviation from the maximally frustrated point brings the system back to
usual -quantized supercurrent. We present detailed analysis of Josepshon
current in the fluctuation-dominated regime (sufficiently long chains) as
function of the chain length, ratio and flux deviation .
We provide estimates for the set of parameters optimized for the observation of
-supercurrent.Comment: 23 pages, 9 figure
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