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Experimental studies of noncentrosymmetric superconductors
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Mayoh, Daniel (2019) Experimental studies of noncentrosymmetric superconductors. PhD thesis, University of Warwick.
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WRAP_Theses_Mayoh_2019.pdf - Submitted Version - Requires a PDF viewer. Download (6Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b3494271~S15
Abstract
Noncentrosymmetric (NCS) superconductors lack a centre of inversion symmetry. This along with antisymmetric spin orbit coupling can result in an admixture of singlet and triplet pairing in the superconducting state. This admixture can give rise to several unconventional superconducting behaviours such as exotic superconducting gap functions, upper critical fields that violate the Pauli limiting field and time-reversal symmetry breaking among others. In this thesis, the NCS superconductors Re6Zr, La7Pd3, La7Ir3, TaRh2B2 and NbRh2B2 have been studied using a combination of low-temperature magnetisation, heat capacity, resistivity and muon spin spectroscopy techniques (μSR).
High quality single crystal and polycrystalline samples have been prepared by a variety of synthesis techniques. Polycrystalline samples of Re6Zr and La7Pd3 were prepared by arc melting. Polycrystalline samples of NbRh2B2 and TaRh2B2 have been synthesised by solid state reaction. Single crystal samples of La7Ir3 have been prepared using the Czochralski process.
The superconducting and normal-state properties of the cubic NCS superconductor Re6Zr with Tc = 6:75(5) K have been investigated. The properties of Re6Zr are observed to be dominated by the effects of disorder with electrical resistivity measurements indicating poor metallic behaviour. Heat capacity measurements of Re6Zr indicate that the superconducting gap is isotropic and s-wave in nature with enhanced electron-phonon coupling.
La7Pd3 and La7Ir3 are hexagonal NCS superconductors with Tc of 1:46(5) and 2:41(5) K respectively. Magnetisation, resistivity, heat capacity and transverse- field μSR measurements of polycrystalline La7Pd3 reveal that it is a fully gapped s-wave superconductor. However, zero-field μSR measurements indicate that timereversal symmetry is broken in the superconducting state. La7Ir3 single crystals have been synthesised and characterised to look for evidence of anisotropy in the superuid density to explain the observation of time-reversal symmetry breaking in polycrystalline samples.
TaRh2B2 and NbRh2B2 are isostructural chiral NCS superconductors with a Tc of 6:05(5) and 7:58(5) K respectively. Both compounds have upper critical fields that violate the Pauli limiting field which can not be modelled by the Werthamer- Helfand-Hohenberg model. Evidence for multigap superconductivity has been found in heat capacity and μSR measurements performed on TaRh2B2 and NbRh2B2.
| Item Type: | Thesis (PhD) | ||||
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| Subjects: | Q Science > QC Physics | ||||
| Library of Congress Subject Headings (LCSH): | Superconductors, Superconductivity, Muon spin rotation | ||||
| Official Date: | July 2019 | ||||
| Dates: |
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| Institution: | University of Warwick | ||||
| Theses Department: | Department of Physics | ||||
| Thesis Type: | PhD | ||||
| Publication Status: | Unpublished | ||||
| Supervisor(s)/Advisor: | Lees, Martin R. ; Balakrishnan, Geetha | ||||
| Format of File: | |||||
| Extent: | xxiv, 124 leaves : illustrations, charts | ||||
| Language: | eng |
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