COOPER–PAIR SUPERFLUID STATE IN HIGH-TEMPERATURE SUPERCONDUCTORS

Abstract

We propose a lattice model of high-temperature superconductors based on their intrinsic granular-like structure. Due to the shortness of the coherent length in high-temperature superconductors, the superconducting order parameter can be well defined locally only in small regions, in which the number and the phase of the Cooper–pairs will experience strong quantum fluctuations. The "superconducting order parameter" in terms of the local number and phase operators of the Cooper–pairs is then regarded as an effective quantized bosonic field described by a discretized Ginzberg–Landau-type effective Hamiltonian, first proposed for granular superconductors and recently for high-temperature superconductors. The effective Hamiltonian also describes the quantum fluctuations of the superconducting order parameter. The global superconducting order sets in when the Cooper–pairs are in the superfluid state. This is in contrast to the previous picture, in which the phase coherence drives the system into the superconducting state when only the phase fluctuations of the superconducting order parameter are considered.