doi: 10.1209/0295-5075/80/47004 Effect of a Zeeman field on the transition from superconductivity to ferromagnetism in metallic grains

PACS 74.20.-z – Theories and models of superconducting state PACS 75.75.+a – Magnetic properties of nanostructures PACS 74.78.Na – Mesoscopic and nanoscale systems 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. Copyright c © EPLA, 2007 Introduction. – The hallmark of the BCS model of superconductivity in metals is the presence of an exci-tation gap ∆. This gap is caused by the formation o