Michael completed his Ph.D in the summer of 2014 on the subject of non-centrosymmetric superconductors and related systems, under the supervision of Prof. Geetha Balakrishnan and Prof. Don Paul.
Michael now works as a Postdoctoral Resesarch Fellow in the Centre for Correlated Matter at Zhejiang University, China.
'Investigations of the superconducting states of noncentrosymmetric LaPdSi3 and LaPtSi3', M. Smidman, A. D. Hillier, D. T. Adroja, M. R. Lees, V. K. Anand, R. P. Singh, R. I. Smith, D. M. Paul and G. Balakrishnan, Physical Review B, 89, 094509 (2014).
'Neutron scattering and muon spin relaxation measurements of the noncentrosymmetric antiferromagnet CeCoGe3', M. Smidman, D. T. Adroja, A. D. Hillier, L. C. Chapon, J. W. Taylor, V. K. Anand, R. P. Singh, M. R. Lees, E. A. Goremychkin, M. M. Koza, V. V. Krishnamurthy. D. M. Paul and G. Balakrishnan, Physical Review B, 88, 134416 (2013).
'Crystal growth of the non-centrosymmetric superconductor Nb0.18Re0.82', R. P. Singh, M. Smidman, M. R. Lees, D. M. Paul and G. Balakrishnan, Journal of Crystal Growth, 361, pp 129 – 131 (2012).
'Is CeCoSi3 a superconductor?', M. Smidman, R. P. Singh, M. R. Lees, D. M. Paul, D. T. Adroja and G. Balakrishnan, Journal of Physics: Conference Series, 391, 012068 (2012).
Thesis Title: Superconducting and magnetic properties of non-centrosymmetric systems - PDF (35.0 MB) (awarded a Physics Department Thesis Prize for 2015).
Non-centrosymmetric superconductors (NCS) and related compounds have been studied using magnetic, specific heat and transport measurements as well as by neutron scattering and muon spin relaxation/rotation (μSR). The crystal structures of NCS lack inversion symmetry and in the presence of a finite antisymmetric spin-orbit coupling, the Cooper pairs are a mixture of spin-singlet and spin-triplet states. In particular, the cerium based NCS have been reported to display unconventional superconductivity. Two different approaches for studying NCS are used. Firstly, the ground states of materials in the CeTX3 (T = transition metal, X = Si or Ge) family have been studied. CeCoGe3 is an antiferromagnet at ambient pressures and becomes superconducting at p > 4.3 GPa and was studied using inelastic neutron scattering (INS), muon spin relaxation/rotation (μSR), neutron diffraction and magnetic susceptibility measurements. The crystal electric fields (CEF) were studied using INS and magnetic susceptibility and the CEF scheme was evaluated. From this a ground state magnetic moment of 1.01 μB/Ce along the c axis was predicted. However, a magnetic moment of 0.405 μB/Ce along the c axis was observed in single crystal neutron diffraction measurements, indicating a reduced magnetic moment due to hybridization between the cerium f-electrons and the conduction band. The INS response was compared to the isostructural CePdSi3, CePtSi3 and CeRuSi3. The former two order antiferromagnetically and the Kondo temperatures were evaluated from the quasielastic scattering. CeRuSi3 is non-magnetic and there is a broad peak in the magnetic scattering at 59 meV. Another approach is to study weakly correlated NCS to look for evidence of unconventional behaviour. In particular, systems where the spin-orbit coupling can be varied by the substitution of heavier atoms into non-centrosymmetric positions were considered. LaPdSi3 and LaPtSi3 are superconductors with Tc = 2.65 and 1.52 K respectively and crystallize in the same crystal structure as the CeTX3 compounds. Magnetization, specific heat and μSR measurements reveal that both compounds are weakly coupled, fully gapped s-wave superconductors but LaPdSi3 is a type-I material while LaPtSi3 is type-II with a Ginzburg-Landau parameter of 2.49. The superconducting properties of single crystals of Nb0.18Re0.82 have been investigated and are discussed.