Volume 80, Number 4, November 2007
Article Number 47004
Number of page(s) 6
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 31 October 2007
EPL, 80 (2007) 47004
DOI: 10.1209/0295-5075/80/47004

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

S. Schmidt1, Y. Alhassid1 and K. Van Houcke2

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 in final form 26 September 2007; published November 2007
published online 31 October 2007

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.

74.20.-z - Theories and models of superconducting state.
75.75.+a - Magnetic properties of nanostructures.
74.78.Na - Mesoscopic and nanoscale systems.

© Europhysics Letters Association 2007