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 neighbouring layers, are an ideal medium in which to explore the interaction of the two order parameters at the interface.

St Andrews is currently collaborating on these systems with the University of Leeds, the University of Bath and the Paul Scherrer Insitute in Switzerland. The collaboration includes expertise in sample growth, nanolithography, theory, and advanced characterisation including scanning Hall-probe microscopy and neutron, muon and X-ray techniques. The St Andrews part of the programme is focussed on the use of neutron techniques, the unique low energy muon (LEM) facility at the Paul Scherrer Institute (PSI), Switzerland and advanced Synchrotron techniques. The aim of the project is use advanced characterisation to understand and control novel ground states in hybrid superconducting-magnetic devices produced using a combination of thin film growth and nanolithograph. They key novely of the project is to use a range of techniques to image, in the broadest sense, signatures of these exotic ground states, in order to provide unique insight into these systems.

The LEM facility at the Paul Scherrer Institute

Continuously tuneable critical current in superconductor-ferromagnet multilayers
P.J Curran J. Kim, N. Satchell, J.D.S. Witt, G. Burnell, M.G Flokstra, S.L. Lee, and S.J. Bending
Appl. Phys. Lett. , 110, 262601 (2017)

Control of superconductivity with a single ferromagnetic layer in niobium/erbium bilayers
N. Satchell, J.D.S. Witt, M.G. Flokstra, S.L. Lee, J.F.K. Cooper, C.J. Kinane, S. Langridge, and G. Burnell
Phys. Rev. Appl., 7  044031 (2017)

Remotely induced magnetism in a normal metalusing a superconducting spin-valve,
M. G. Flokstra, N. Satchell, J. Kim, G. Burnell, P. J. Curran, S. J. Bending, J. F. K. Cooper, C. J. Kinane, S. Langridge, A. Isidori, N. Pugach, M. Eschrig, H. Luetkens, A. Suter, T. Prokscha and S. L. Lee,
Nat. Phys. 12 , 57-61 (2016).

Intrinsic Paramagnetic Meissner Effect Due to s-Wave Odd-Frequency Superconductivity,
A. Di Bernardo, Z. Salman, X. L. Wang, M. Amado, M. Egilmez, M. G. Flokstra, A. Suter,2 S. L. Lee, J. H. Zhao,
T. Prokscha, E. Morenzoni, M. G. Blamire, J. Linder, and J.W. A. Robinson,
PHYSICAL REVIEW X 5, 041021 (2015).

Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid,
P. J. Curran, J. Kim, N. Satchell, J. D. S. Witt, G. Burnell, M. G. Flokstra, S. L. Lee, J. F. K. Cooper, C. J. Kinane, S. Langridge, A. Isidori, N. Pugach, M. Eschrig and S. J. Bending,
Applied Physics Letters 107, 262602 (2015).

Controlled suppression of superconductivity by the generation of polarized Cooper pairs in spin-valve structures,
M. G. Flokstra, T. C. Cunningham, J. Kim, N. Satchell, G. Burnell, P. J. Curran, S. J. Bending, C. J. Kinane, J. F. K. Cooper, S. Langridge, A. Isidori, N. Pugach, M. Eschrig, and S. L. Lee
PHYSICAL REVIEW B 91, 060501(R) (2015).