MUON SPIN ROTATION STUDIES OF URU2SI2 AND DICHALCOGENIDE SUPERCONDUCTORS

Abstract

This dissertation details studies of two different material classes: isoelectronically doped URu2Si2, and dichalcogenide superconductors, both of which are primarily studied with the muon spin rotation (μSR) experimental technique.

The objective of the work on URu2Si2 was to probe how the low temperature "hidden order" state, which transitions into antiferromagnetism under hydrostatic pressure, evolves when perturbed by isoelectronic chemical doping. μSR measurements of iron doped URu2Si2, which produces positive chemical pressure, show long range magnetic order. Neutron diffraction measurements demonstrate that this magnetic order is antiferromagnetism, and both muon spin rotation and neutron scattering suggest that the magnetic moment increases with increasing doping in contrast to the pressure independent moment seen in the pressure induced antiferromagnetic state of URu2Si2. Inelastic neutron scattering measurements show a significantly larger commensurate gap at the (1 0 0) position compared to that seen in the pressure induced antiferromagnetic phase. Osmium doping, which gives negative effective chemical pressure, shows similar behaviour in μSR measurements to the iron doped samples. This suggests that these samples are also antiferromagnetic and that the evolution from hidden order to antiferromagnetism is not solely caused by changes in the lattice size. This is further supported by μSR measurements on germanium doped samples that do not show magnetic order despite giving similar negative chemical pressure to the osmium doped samples.

Work on the dichalcogenide superconductors involved using transverse field μSR to measure the temperature dependence of the magnetic penetration depth of two different materials, Pt0.05Ir0.95Te2 and PbTaSe2. The μSR data on Pt0.05Ir0.95Te2 were supplemented by magnetometry measurements of the penetration depth. Zero field μSR measurements were also performed on PbTaSe2, and rule out any time reversal symmetry breaking field greater than 0.05 G. These measurements all suggest that both materials are fully gapped superconductors.