Effect of a Zeeman field on the transition from superconductivity to ferromagnetism in metallic grains

¹  Center for Theoretical Physics, Sloane Physics Laboratory, Yale University - New Haven, CT 06520, USA
²  Universiteit Gent, Vakgroep Subatomaire en Stralingsfysica - Proeftuinstraat 86, B-9000 Gent, Belgium

Received: 1 May 2007
Accepted: 26 September 2007

Abstract

We investigate the competition between pairing correlations and ferromagnetism in small metallic grains in the presence of a Zeeman field. Our analysis is based on the universal Hamiltonian, valid in the limit of large Thouless conductance. We show that the coexistence regime of superconducting and ferromagnetic correlations can be made experimentally accessible by tuning an external Zeeman field. We compare the exact solution of the model with a mean-field theory and find that the latter cannot describe pairing correlations in the intermediate regime. We also study the occurrence of spin jumps across the phase boundary separating the superconducting and coexistence regimes.