2018

Unconventional superconductors with spin-orbit interaction

In this thesis superconductivity and its transport properties are studied in the presence of spin-orbit interaction. Theory building, calculations and simulations, were central in this PhD research.

‘At the Interfaces & Correlated Electrons (ICE) Group, we had lots of fruitful discussions,’ says Tatsuki Hashimoto. ‘I enjoyed my double role: teaching the experimentalists of our Group about the most recent theoretical insights, and me learning from them how to perform experiments in the field: which materials and set-ups they choose, what equipment is available, and how they work towards secure results.’

Tatsuki worked on a double-degree PhD, the other thesis being published and defended at Nagoya University Japan. ‘I learnt that for producing new physics, one cannot look at theory alone,’ Tatsuki says. ‘New experimental strategies are needed, in order to predict and show the presence of the Majorana fermion one day.’

Making new models, calculations and performing simulations from there, is just as exciting as performing actual experiments, thus Tatsuki. ‘I have learnt that progress in my research, is not so much a peak experience, but only made possible by systematically taking small, steady steps. In addition to fundamental science, my work is relevant for novel future quantum computation techniques.’  

In this PhD especially topological materials are considered. These materials are believed a promising platform, to realize unconventional superconductivity, since spin-orbit interactions can support spin-triplet pairing states here.

Dirac Semimetals

‘My results have been published in Physicial Review Letters B,’ Tatsuki says. ‘In one of them Dirac Semimetals are central. A novel phase diagram of superconductivity was created. We have found that, when the inter-orbital attraction is dominant, the unconventional superconducting state with point nodes appears.’

Bulk and surface physical properties of intrinsic superconductivity in doped Dirac semimetals, are described, to verify the experimental signature of possible superconducting states. For example, the temperature dependence of bulk physical properties is calculated, such as electronic specific heat, spin susceptibility and surface states. It has been found that possible superconducting states can be distinguished by combining bulk and surface measurements.

Spin-orbit interaction

Tatsuki: ‘In another publication the complex interactions of unconventional superconductivity, the presence of magnetic fields and nanowires are presented. We showed that in a new geometry device built-up, spin-orbit interaction may change as a result of the nanowires’ electric current. The strength of the spin-orbit interaction can be tuned.’ 

Industry

After his Defense, Tatsuki will be working on a project launched at the ICE Group at Mesa+.

‘After that I prefer to find a job in industry, in Japan,’ he says. ‘By using my knowledge base, skills and experiences, I can be of added value within many types of industrial companies, discovering novel application areas, performing clever experiments and using new samples.’