Abstract
Most superconductors are classified having either spinsinglet or spintriplet pairing. But noncentrosymmetric superconductors (NCSs) lack a centre of inversion. This allows for a large inversionantisymmetric spinorbit coupling (SOC), transforming under symmetry operations according to the crystal point group, throughout the Brillouin zone. The SOC splits the Fermi surface into two sheets having opposite helicity. Due to this splitting both singlet and triplet pairing coexist in NCSs, which has profound effects on the material properties.
In this thesis a comprehensive study of these effects is carried out for materials with tetrahedral Td, tetragonal C4v, and cubic point group O, as well as for several different singlet to triplet order parameter ratios. The superconducting order parameter is calculated using the quasiclassical method of superconductivity, both in the bulk and at a surface. The superconducting instability and the evolution of the gap below Tc are studied in the bulk, and it is shown that a second phase transition is possible for certain parameter values.
The spatially varying order parameters are calculated selfconsistently for a range of different surface orientations in order to determine the orientation's effect on the order parameter suppression. For each selfconsistent order parameter profile the surface density of states is calculated showing intricate structure of the Andreev bound states (ABS) as well as spin polarisation.
Furthermore, the tunnel conductance spectra are computed for different surface normals with two of them exhibiting zerobias conductance peaks (ZBCPs). The zerobias conductance and the ABS are studied in detail showing which quasiclassical trajectories contribute to the ZBCPs. In addition, the zerobias conductance computed is for a range of surface orientations showing the sensitivity of the ZBCPs.
The large SOC in a NCS can endow the material with nontrivial topology, depending on Fermi surface geometry and singlet to triplet ratio. A topological phase diagram is constructed for open and closed Fermi surfaces showing a sharp transition between the two for the point group $O$. Lastly the topology's effect on the surface states is thoroughly investigated.
In this thesis a comprehensive study of these effects is carried out for materials with tetrahedral Td, tetragonal C4v, and cubic point group O, as well as for several different singlet to triplet order parameter ratios. The superconducting order parameter is calculated using the quasiclassical method of superconductivity, both in the bulk and at a surface. The superconducting instability and the evolution of the gap below Tc are studied in the bulk, and it is shown that a second phase transition is possible for certain parameter values.
The spatially varying order parameters are calculated selfconsistently for a range of different surface orientations in order to determine the orientation's effect on the order parameter suppression. For each selfconsistent order parameter profile the surface density of states is calculated showing intricate structure of the Andreev bound states (ABS) as well as spin polarisation.
Furthermore, the tunnel conductance spectra are computed for different surface normals with two of them exhibiting zerobias conductance peaks (ZBCPs). The zerobias conductance and the ABS are studied in detail showing which quasiclassical trajectories contribute to the ZBCPs. In addition, the zerobias conductance computed is for a range of surface orientations showing the sensitivity of the ZBCPs.
The large SOC in a NCS can endow the material with nontrivial topology, depending on Fermi surface geometry and singlet to triplet ratio. A topological phase diagram is constructed for open and closed Fermi surfaces showing a sharp transition between the two for the point group $O$. Lastly the topology's effect on the surface states is thoroughly investigated.
Original language  English 

Qualification  Ph.D. 
Awarding Institution 

Award date  26 May 2016 
Publication status  Unpublished  2016 
Keywords
 superconductor
 topology
 tunnelling
 noncentrosymmetric superconductors
 QUASICLASSICAL EQUATIONS