Nobuhiko Hayashi

Vortex structure in d -wave superconductors

The vortex structure of pure

LOW-LYING QUASIPARTICLE EXCITATIONS AROUND A VORTEX CORE IN QUANTUM LIMIT

{mathit{d}}_{{mathit{x}}^{2}mathrm{ensuremath{-}}{mathit{y}}^{2}}

Direct measurement of electron transfer through a hydrogen bond between single molecules.

-wave superconductors is microscopically analyzed in the framework of the quasiclassical Eilenberger equations. A self-consistent solution for the d-wave pair potential is obtained in the case of an isolated vortex. The vortex core structure, i.e., the pair potential, the supercurrent, and the magnetic field, is found to be fourfold symmetric even in the case that the mixing of the s-wave component is absent. The detailed temperature dependences of these quantities are calculated. The fourfold symmetry becomes clear when the temperature is decreased. The local density of states is calculated for the self-consistently obtained pair potential. From the results, we discuss the flow trajectory of the quasiparticles around a vortex, which is characteristic in

Relation between Vortex Core Charge and Vortex Bound States

{mathit{d}}_{{mathit{x}}^{2}mathrm{ensuremath{-}}{mathit{y}}^{2}}

Star-Shaped Local Density of States around Vortices in a Type-II Superconductor.

-wave superconductors. The experimental relevance of our results to high-temperature superconductors is also given. textcopyright{} 1996 The American Physical Society.

Local density of states in the vortex lattice in a type II superconductor

Focusing on a quantum-limit behavior, we study a single vortex in a clean s-wave type-II superconductor by self-consistently solving the Bogoliubov-de Gennes equation. The discrete energy levels of the vortex bound states in the quantum limit is discussed. The vortex core radius shrinks monotonically up to an atomic-scale length on lowering the temperature T, and the shrinkage stops to saturate at a lower T. The pair potential, supercurrent, and local density of states around the vortex exhibit Friedel-like oscillations. The local density of states has particle-hole asymmetry induced by the vortex. These are potentially observed directly by STM.

S- AND DXY-WAVE COMPONENTS INDUCED AROUND A VORTEX IN DX2-Y2-WAVE SUPERCONDUCTORS

Understanding electron transfer (ET) from a single molecule to another single molecule holds essential importance to realize bottom-up molecular devices in which constituent molecules are self-assembled via noncovalent interactions between each other. However, rather little is currently known about the ET properties at the single-molecule interface. Here we employ molecular tips to quantify the ET through a H-bond between single molecules. We found that a H-bond conducts electrons better than a covalent σ bond at short-range. Its conductance, however, decays steeply as the chain length of the H-bonded molecules increases. First-principle calculations were performed to reveal the electronic origin of the facile ET through the H-bond. Our results demonstrate that H-bonding in a molecular junction significantly affects its transport property.

Effects of gap anisotropy upon the electronic structure around a superconducting vortex

Spatially inhomogeneous electron distribution around a single vortex is discussed on the basis of the Bogoliubov-de Gennes theory. The spatial structure and temperature dependence of the electron density around the vortex are presented. A relation between the vortex core charge and the vortex bound states (or the Caroli-de Gennes-Matricon states) is pointed out. Using the scanning tunneling microscope, information on the vortex core charge can be extracted through this relation.

Elementary vortex pinning potential in superconductors with unconventional order parameter

The electronic structure of vortices in a type II superconductor is analyzed within the quasiclassical Eilenberger framework. The possible origin of a sixfold {open_quote}{open_quote}star{close_quote}{close_quote} shape of the local density of states, observed by scanning tunneling microscope (STM) experiments on NbSe{sub 2}, is examined in the light of the three effects: the anisotropic pairing, the vortex lattice, and the anisotropic density of states at the Fermi surface. Outstanding features of split parallel rays of this star are well explained in terms of an anisotropic {ital s}-wave pairing. This reveals not only a rich internal electronic structure associated with a vortex core, but also unique ability of the STM spectroscopy. {copyright} {ital 1996 The American Physical Society.}

Fundamental Properties of a Vortex in a d-Wave Superconductor

Local density of states (LDOS) in the triangular vortex lattice is investigated based on the quasi-classical Eilenberger theory. We consider the case of an isotropic s-wave superconductor with the material parameter appropriate to NbSe_2. At a weak magnetic field, the spatial variation of the LDOS shows cylindrical structure around a vortex core. On the other hand, at a high field where the core regions substantially overlap each other, the LDOS is sixfold star-shaped structure due to the vortex lattice effect. The orientation of the star coincides with the experimental data of the scanning tunneling microscopy. That is, the ray of the star extends toward the nearest-neighbor (next nearest-neighbor) vortex direction at higher (lower) energy.