1. Department of Physics, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
2. Materials Science Centre, University of Groningen, Nigenborgh 4, 9747AG, The Netherlands
3. Département de Recherche Fondamentale sur la Matière condensée - SPSMS, CEA Grenoble, 17 Av. des Martyrs, Grenoble 38054, France
4. Present address: MPI Chemische Physik fester Stoffe, Bayreuther Str. 40, 01189 Dresden, Germany (F.M.G.); Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (S.S.S.).

Correspondence to: G. G. Lonzarich¹ Correspondence and requests for materials should be addressed to G.G.L. (e-mail: Email: ltp-secretary@phy.cam.ac.uk).

Abstract

The absence of simple examples of superconductivity adjoining itinerant-electron ferromagnetism in the phase diagram has for many years cast doubt on the validity of conventional models of magnetically mediated superconductivity. On closer examination, however, very few systems have been studied in the extreme conditions of purity, proximity to the ferromagnetic state and very low temperatures required to test the theory definitively. Here we report the observation of superconductivity on the border of ferromagnetism in a pure system, UGe ₂, which is known to be qualitatively similar to the classic d-electron ferromagnets. The superconductivity that we observe below 1 K, in a limited pressure range on the border of ferromagnetism, seems to arise from the same electrons that produce band magnetism. In this case, superconductivity is most naturally understood in terms of magnetic as opposed to lattice interactions, and by a spin-triplet rather than the spin-singlet pairing normally associated with nearly antiferromagnetic metals.

1. Department of Physics, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
2. Materials Science Centre, University of Groningen, Nigenborgh 4, 9747AG, The Netherlands
3. Département de Recherche Fondamentale sur la Matière condensée - SPSMS, CEA Grenoble, 17 Av. des Martyrs, Grenoble 38054, France
4. Present address: MPI Chemische Physik fester Stoffe, Bayreuther Str. 40, 01189 Dresden, Germany (F.M.G.); Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK (S.S.S.).

Correspondence to: G. G. Lonzarich¹ Correspondence and requests for materials should be addressed to G.G.L. (e-mail: Email: ltp-secretary@phy.cam.ac.uk).