The competition between superconducting and magnetic order is a long-standing question in condensed matter physics.  These two forms of order are usually mutually exclusive, and are found to coexist in relatively few materials. The situation is particularly intriguing when the same electrons are involved in both forms of order, since this indicates new and exotic descriptions of the superconducting state.  Artificially fabricated multilayered thin-film structures, where superconducting (S) and ferromagnetic (FM) materials are juxtaposed in neighboring layers, are an ideal medium in which to explore the interaction of the two order parameters at the interface.

We are currently using polarised neutron reflectivity (PNR) combined with low energy muon spin rotation (LEM) to study the coexistence of magnetism in thin films. When Uusing LEM, the energy of the muon can be controlled to vary the implantation depth of the muon into the sample. In this way, one is able to measure the local fields in different layers of the sample. By studying the electrons in the vicinity of the interface between a magnetic and a superconducting layer in an artificially fabricated thin film structure, we have recently observed a modified spin density wave coexisting with superconductivity. Moreover, this spin density wave adjusts to accommodate the onset of superconductivity. This intimate coupling of the two order parameters has profound implications for theoretical descriptions of this and similar systems. This type of coupling could even lead to novel applications in hybrid magnetic-superconducting devices.

References

Magnetic field distributions in thin film superconducting samples, S. L. Lee, A. Drew, C. H. Marrows, A. Potenza, Science Highlights, ISIS Annual Report (2003).

Coexistence and Coupling of Superconductivity and Magnetism in Thin Film Structures, A. Drew, S. L. Lee, U. K Divakar, D. Charalambous, A. Potenza, C. Marrows, H. Luetkens, A. Suter, T Prokscha, R. Khasanov , E. Morenzoni, D. Ucko, E. M.Forgan, Phys. Rev. Lett. 95 197201 (2005).

The LEM facility at the Paul Scherrer Institut