Open Collections

Kramer-Pesch effect in LuNi2B2C

University of British Columbia

This thesis describes pSR observations of the internal magnetic field distribution n{B) as a function of temperature in LuNi₂B₂C (T[sub c] = 16.0 K, H[sub c2](0) = 7T), under a magnetic field of H = 1.2T applied parallel to the crystal c axis. The pSR 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 λ(T) 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 λ with rising temperature. The rate of any such linear growth, however, is smaller than would be expected for an energy gap Δ with line nodes. The fitted core radius temperature dependence p(T) reveals a Kramer-Pesch effect, or linear contraction of the vortex core radius p upon cooling at low temperatures T << T[sub c] , 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 NbSe₂, implying that quasiparticles behave similarly in LuNi₂B₂C and NbSe₂ despite their different dimensionalities, and that longitudinal disorder of vortices has negligible impact on μSR determinations of the vortex core radius p. 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.

Thesis/Dissertation

application/pdf

2009-08-06

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

http://hdl.handle.net/2429/11788

Astronomy

University of British Columbia

UBCV

DSpace