Hisataka Suematsu

Vortex Molecule in a Nanoscopic Square Superconducting Plate

Using the finite element method and solving the Bogoliubov–de Gennes equation, we have investigated magnetic field dependence of the stable vortex structures in a mesoscopic superconducting plate at low temperature ( T = 0.1 T c ). Because of the compactness of vortex configuration, there is interference between bound states around vortices and such quasi-particle structure affects the vortex configuration. Especially in two-vortices state, vortices form a molecule-like state, where bound states of each vortex form molecular orbital like bonding and anti-bonding states. The vortex configuration is different from that, which is expected from the repulsive interaction between vortices.

Critical temperature in nanoscopic superconductors

Recently, we have studied the properties of nano-scale superconductors different from that of bulk superconductors. One of the properties is the critical temperature of normal-superconducting transition. We evaluate the critical temperature with two method by solving Bogoliubov-de Gennes equation. The former method is the general approximation calculation, which is good approximation in bulk superconductors. The latter is the direct calculation of the T-dependence of the order parameter A by solving the Bogoliubov-de Gennes equation self-consistently. These methods lead to the much different critical temperature and the true critical temperature is higher than we expect in the bulk superconductors.

Quasi‐particle Spectrum of Nano‐scale Superconductors under External Magnetic Field

We have solved the Bogoliubov‐de Gennes equation of nano scale superconducting square plate under an external magnetic field. The result shows that multiple‐vortex states become stable at low temperature. In these states, vortex bound states of these vortices interfere with each other and the vortices form a kind of vortex molecule, and this is reflected in the local density of states.

Self‐Consistent Solution of the Bogoliubov‐de Gennes Equation for a Single Vortex in f‐wave Superconductors: Application to Sr2RuO4

The paring sysmmetry of the triplet superconductor Sr2RuO4 is still controversial. Recently, the scanning tunneling microscopy measurement has been done on the quasi‐particle structure in Sr2RuO4. They obtained the local density of states around a single vortex. Using the Bogoliubov‐de Gennes equation in the differential form off‐wave (Δ± (k) = Δd (kx ± ky) cos (ckz)) superconductivity that has the horizontal nodes, we investigate the quasi‐particle structure. As compared with the p‐wave pairing, the local density of states of f‐wave paring at the vortex core is much similar to the experimental data.