SANS investigations of the flux line lattice in unconventional superconductors

Small-angle neutron scattering has been used to study the flux line lattice (FLL) in the \(d\)-wave superconductors YBa₂Cu₃O₇ and CeCoIn₅. Our studies on the High-T_c superconductor YBa₂Cu₃O₇ were carried out using a twin-free sample, and we present the first observations of the intrinsic FLL structure in this material, with a magnetic field applied parallel to the crystal c-axis (H || c). We observe a sequence of field-driven FLL structure transitions, the detailed physics of which can be broadly described in terms of field-induced non-locality, the potency of which is perhaps increased by the anisotropy of the order-parameter. The heavy-fermion superconductor CeCoIn₅ exhibits an exotic ground state that combines unconventional superconductivity with strong paramagnetism. With H || c, these properties contribute towards both a rich FLL structure phase diagram, and new behaviour of the FLL form factor. Most notably, we observe the form factor to increase with field, in strong contrast to the monotonic decrease expected from predictions made using more conventional theories. These results can be qualitatively described by calculations made within the framework of the quasiclassical Eilenberger theory, which indicate the increase in the form factor as due to field-induced Pauli paramagnetic effects which manifest most strongly within the flux line cores.

Name dc:type.qualificationname

d_ph

Level dc:type.qualificationlevel

d_ph

Grantor dc:publisher.institution

University of Birmingham

Year dc:date.issued

2009

Author dc:creator

• White, Jonathan Stuart

• QC Physics

Repository record dc:identifier.uri

http://etheses.bham.ac.uk//id/eprint/319/2/Decl_IS_White09PhD.jpg

OAI identifier oai:identifier

oai:etheses.bham.ac.uk:319