Yuhei Niwa

Quasi-particle spectrum around half-quantum vortices (HQVs) in triplet superconductors

It is shown recently triplet superconductors like Sr2RuO4, UPt3 and PrOs4Sb12 have Majorana fermion, d-soliton and half-quantum vortices (HQVs). The Bogoliubov de Gennes (BdG) equation necessary for the present purpose is derived following Ivanov. For H Pc and d-vector in the ab plane the one of HQVs has a series of bound states including the zero-energy-mode or Majorana fermion while the other has no bound state for a single spin component. We illustrate this for p-wave SC.

Magnetic Flux Structures in Nano-sized Multiband Superconductors

Magnetic flux structures of nano-sized two gap superconducting square plate under an external field are investigated using the two-band Bogoliubov-de Gennes equations and the finite element method. The vortex structures are different from those for a single-gap s-wave superconductor. The vortex is bound around the boundaries because of type I component of the order parameters. This is the special feature of the type 1.5 superconductor.

Appearance of Magnetization around a Pair of Half-Quantum Vortices in Chiral p-Wave Superconductors

We have investigated quasi-particle excitations around a pair of half-quantum vortices in chiral \(p\)-wave superconductors, using the Bogoliubov–de Gennes equations. We use the elliptic coordinates and the Mathieu function for numerical calculations. We found that the height of peak of a local density of states of the bound states for the half-quantum vortex core is a half of that for a singly quantized vortex core. Also, it was found that a magnetization appears along a pair of half-quantum vortices. Existence of half-quantum vortex might be confirmed by observation of this distribution of the magnetization.

Microscopic Investigation of Vortex-Vortex Interaction in Conventional Superconductors

Quasi-particle structures around a pair of vortices and its effect on the vortex-vortex interaction are investigated. For this purpose, a new numerical method is developed. This method uses the elliptic coordinate and (modified) Mathieu functions. Using this method and solving the Bogoliubov-de Gennes equation, we analyse how quasi-particle structures change with the vortex-vortex distance.

Quasi-particle structures around a pair of half-quantum vortices in chiral p-wave super conductors

Quasi-particle structures around a pair of half-quantum vortices (HQVs) and two singly quantized vortices are investigated, using the Bogoliubov-de Gennes equation. For this purpose, a new numerical method, which incorporates the two phase singularity points, is developed, using elliptic coordinates and the (modified) Mathieu functions. We investigate the local density of states around two singly quantized vortices and a pair of HQVs in chiral p-wave superconductors. As a result, we found that there is a difference between them: Quasiparticle bound states interfere with each other for two singly quantized vortices case and do not for a pair of HQVs case.