The mechanism of unconventional superconductivity is still mysterious, despite extensive studies. Muon spectroscopy (μSR) and small angle neutron scattering (SANS) studies of some unconventional superconductors were carried out. The NCS superconductors: Ru7B3 and α-BiPd, Heusler compounds: ZrNi2Ga and NbNi2Ga and the marginal superconductor ZrB12 were investigated. This thesis reports new phenomena observed in those systems and advances the knowledge of the ground state properties of unconventional superconductors. Polycrystalline samples and single crystals of the non-centrosymmetric superconductor (NCS) Ru7B3 were studied. Evidence for time-reversal symmetry (TRS) breaking in the superconducting state of Ru7B3 were found using μSR. So far, it is the third known NCS superconductor which breaks TRS. Potentially multigap behaviour was observed. The presence of two distinct superconducting gaps was suggested in polycrystalline Ru7B3 using μSR. Additionally, SANS and μSR measurements indicate unusual behaviour for the observed distorted hexagonal flux line lattice (FLL) in Ru7B3, yet the nature of this behaviour remains inconclusive. μSR studies of another NCS superconductor α-BiPd give evidence that two superconducting gaps are present in α-BiPd, either two s-wave gaps or s-wave and d-wave gaps exist in α-BiPd. Additionally, unusual temperature evolution of the upper critical field of α-BiPd was observed. Two superconducting compounds belonging to the Heusler family, ZrNi2Ga and NbNi2Ga, were investigated using μSR. Temperature dependence of the penetration depth of ZrNi2Ga suggests an s-wave, conventional behaviour in this superconductor. Evidence of a structural change in the morphology of the FLL was observed: a square FLL potentially exists at low temperatures and a hexagonal FLL is present closer to Tc. Additionally, μSR experiments suggest that TRS is preserved in both measured Heusler compounds. SANS studies of a marginal, low-k superconductor ZrB12 were carried out. SANS studies were performed in a range of temperature and magnetic field so to access different parts of the superconducting phase diagram of ZrB12. A square vortex lattice was found in all measured temperatures and fields.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:647957 |
| Date | January 2014 |
| Creators | Parzyk, Natalia A. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/67561/ |
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