Magnetic fields penetrate superconductors as quantized tubes of magnetic flux, or vortices. A transport current passed through such a superconductor exerts a transverse force on the vortices. The dissipation resulting from vortex motion is characterized by a vortex viscosity, and microwave techniques provide a powerful means of accessing this in the presence of pinning. A novel microwave spectroscopy apparatus has been set up that allows sensitive measurements of the dynamical properties of vortices to be made at temperatures down to 80 mK, in magnetic fields up to 9 T, and at frequencies from 2.25 to 25 GHz. A comprehensive study has been carried out at 2.5 GHz on the heavy fermion superconductor CeCoIn5. Surprising new behaviour is revealed in the vortex viscosity, which, at low fields, exhibits clear signatures of d-wave quasiparticle physics. This suggests that delocalized excitations outside the vortex cores are predominantly responsible for vortex dissipation in CeCoIn5.
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Thesis advisor: Broun, David
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