This thesis describes SR observations of the internal magnetic field
distribution *n*(*B*) as a function of temperature in LuNi_{2}B_{2}C (
,
), under a magnetic field of
applied parallel to the crystal axis. The SR
polarisation signal is fitted to a
nonlocal London model, assuming a square vortex lattice. By
incorporating first order nonlocal corrections, this model achieves
significantly better fits than the local London model. The fitted penetration
depth temperature dependence
follows the form expected for a BCS
*s*-wave superconductor, although the dependence is also consistent with a
slight linear increase in the penetration depth
with rising
temperature. The rate of any such
linear growth, however, is smaller than would be expected for an energy
gap
with line nodes. The fitted core radius temperature
dependence
reveals a Kramer-Pesch effect, or linear contraction of the
vortex core radius
upon cooling at low temperatures ,
that is
weaker than predicted. The Kramer-Pesch effect found for this nearly
three-dimensional superconductor is almost identical to that seen in
quasi two-dimensional NbSe_{2}, implying that quasiparticles behave similarly
in LuNi_{2}B_{2}C and NbSe_{2} despite their different dimensionalities, and
that longitudinal disorder of vortices has negligible impact on SR
determinations of the vortex core radius .
The surprisingly small
magnitude of the Kramer-Pesch effect suggests
that future theoretical work on the temperature dependence of vortex structure
should consider zero point motion of vortices and intervortex interactions.

2001-10-31