Physics – Condensed Matter – Statistical Mechanics
Scientific paper
1999-03-15
Physical Review B60, 7473 (1999)
Physics
Condensed Matter
Statistical Mechanics
18 pages, four Postscript figures, REVTEX style, Physical Review B 1999. We have added one important reference to this version
Scientific paper
10.1103/PhysRevB.60.7473
We have studied a quantum Hamiltonian that models an array of ultrasmall Josephson junctions with short range Josephson couplings, $E_J$, and charging energies, $E_C$, due to the small capacitance of the junctions. We derive a new effective quantum spherical model for the array Hamiltonian. As an application we start by approximating the capacitance matrix by its self-capacitive limit and in the presence of an external uniform background of charges, $q_x$. In this limit we obtain the zero-temperature superconductor-insulator phase diagram, $E_J^{\rm crit}(E_C,q_x)$, that improves upon previous theoretical results that used a mean field theory approximation. Next we obtain a closed-form expression for the conductivity of a square array, and derive a universal scaling relation valid about the zero--temperature quantum critical point. In the latter regime the energy scale is determined by temperature and we establish universal scaling forms for the frequency dependence of the conductivity.
José Jorge V.
Kopec Tadeusz. K.
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