JOSEPHSON ARRAY OF MESOSCOPIC OBJECTS - MODULATION OF SYSTEM PROPERTIES THROUGH THE CHEMICAL-POTENTIAL

The phase diagram of a two-dimensional Josephson array of mesoscopic o bjects (superconducting granules, superfluid helium in a porous medium , traps with Bose-condensed atoms, etc.) is examined. Quantum fluctuat ions in both the modulus and phase of the superconducting order parame ter are taken into account within a lattice boson Hubbard model. Modul ating the average occupation number no of the sites in the system (the ''number of Cooper pairs'' per granule, the number of atoms in a trap , etc.) leads to changes in the state of the array, and the character of these changes depends significantly on the region of the phase diag ram being examined. In the region where there are large quantum fluctu ations in the phase of the superconducting order parameter, variation of the chemical potential causes oscillations with alternating superco nducting (superfluid) and normal states of the array. On the other han d, in the region where the bosons interact weakly, the properties of t he system depend monotonically on no. Lowering the temperature and inc reasing the particle interaction force lead to a reduction in the widt h of the region of variation in no within which the system properties depend weakly on the average occupation number. The phase diagram of t he array is obtained by mapping this quantum system onto a classical t wo-dimensional XY model with a renormalized Josephson coupling constan t and is consistent with our quantum path-integral Monte Carlo calcula tions. (C) 1998 American Institute of Physics. [S1063-7761(98)01608-4] .