Observation of an anomalous Superconducting State under high magnetic fields - Experimental evidence for the FFLO superconducting state -

A France-Japan-US collaborative research group (H. Mayaffre, S. Kramer, M. Horvatic', C. Berthier at Laboratoire National de Champs Magne'tiques Intenses, France; K. Miyagawa, K. Kanoda at Department of Applied Physics, University of Tokyo, Japan; V. F. Mitrovic'at Brown University, USA) succeeded in observing the sought-after peculiar superconducting state (called FFLO state), that survives under strong magnetic fields.

Because an electric current can flow without dissipative heating in a superconducting material, the superconductivity has been studied intensively in both fundamental and application researches. While superconducting materials are used under magnetic field, the strong magnetic field generally destroys the superconducting state. So, the behaviors of superconductors under magnetic field are of keen interest. Electrons that carry charges and minute magnets called spins form pairs with the spins aligned anti-parallel(the Cooper pairs) in a superconducting state. An external magnetic field induces the motion of the Cooper pairs and forces the spins to align parallel to the field direction. Both effects act to break the Cooper pairs so that the strong magnetic field will destroy the superconductivity. However, even in such destructively high fields, a peculiar superconducting state called FFLO　(Fulde-Ferrell-Larkin-Ovchinnikov) state, was predicted to be able to survive by spatially undulating the density of Cooper pairs. There has been This state has long been sought after experimentally but the existence has still been unclear.

 The research group has investigated the organic superconductor under high magnetic fields by means of the NMR technique and captures evidence for the FFLO state. This finding gives to the application area a hint to overcome the limitation of field restricted  by the conventional mechanism.