Tadashi Takemori

Optical Response of a Sphere Coupled to a Metal Substrate

Optical response of a sphere placed above a flat Ag substrate is calculated. Local dielectric constants are assumed and exact account is taken of the retardation effect. For a Ag sphere above a Ag substrate, coupling of sphere and substrate plasmons results in a strong local field, whereby Raman scattering by molecules on the sphere surface is enhanced by a factor of 10 8 . The case of a dielectric sphere is also discussed. The mechanism is understood in terms of surface plasmon polariton excitation.

2-D Oxygen Order in the 55 K-Superconducting Phase of Y-Ba-Cu-O

Considering the nearest- and two next-nearest-neighbor interactions, phase diagrams are presented for oxygens in the middle layer of Y-Ba-Cu-O. A simple estimate indicates it is likely that the oxygens in the 55 K-phase are formed from the 90 K-phase by removing all oxygen atoms from every other Cu-O chain.

Generalized Fibonacci lattice dynamical trace map, invariant and quasi-invariant

Abstract Dynamical trace map of the tight-binding model is investigated for the generalized Fibonacci lattice characterized by the stacking rule S ( n +1)= S ( n ) p S ( n −1) q with p,q integers, where S(n) is the atomic sequence of the n-th generation. An expression is found of a quasi-invariant which is valid for any set of (p,q) and also of the invariant of the trace map for q=1 and q = p +1. Average density of states is calculated for p=2, q=1, 2 and 3.

Inter-layer pairing of two-dimensional electrons

Abstract We point out the possibility that the high transition temperatures of the recently discovered oxide superconductors are dominantly caused by the inter-layer Cooper pairing of two-dimensional electrons that are coupled through the exchange of three-dimensional phonons.

Theory of Superconductivity of Inter-Layer Cooper Pairing

An inter-layer Cooper pairing mechanism is considered for layers of two-dimensional electrons which are coupled by the exchange of three-dimensional phonons.We propose that the high transition temperature of Ba-Y-Cu-O compound may originate from this mechanism because of the combined effects of the strong attraction due to phonon exchange and the substantially reduced Coulomb repulsion between paired electrons. Impurity effects and relative stability between the inter- and intra-layer Cooper pairings are discussed and a phase diagram is calculated.

Field enhancement in a spherical cavity beneath a metal surface

We have solved Maxwells equation around a spherical cavity just beneath a flat surface of a Ag substrate. We use dielectric constant by Johnson and Christy. A strong field enhancement is found on a small area of cavity surface closest to the substrate surface where the metal layer is thin. The enhancement mechanism is the induced surface plasma oscillation on the thin Ag layer. Raman enhancement factor of order 10 4 is found for a cavity of radius 100 A centered 110 A beneath the substrate surface.

Electronic Structure of Generalized Fibonacci Lattices.I.Invariant,Quasi-Invariant and Cyclic Orbits

Dynamical trace-map of the tight-binding model is investigated by generalizing the stacking rule of the Fibonacci lattice. The recurrence relation is defined by D ( n +1)= D ( n ) p D ( n -1) q for positive integers p and q , where D ( n ) is the atomic sequence of the n -th generation. The structure of the dynamical trace-map is analyzed in terms of the invariant and the quasi-invariant of the map. Characteristic features of the wave function, local density of states and the average density of states are analyzed.

Fast algorithm for calculating nonlinear response functions of large quantum systems and its application to TPA spectra

We review the progress we have been making in recent years in the application of the real-time real-space higher-order finite-difference method to the calculation of various linear/nonlinear response functions. The method was devised for numerical calculation of electronic properties of large quantum systems, and has so far been applied primarily to the calculation of dielectric functions. However, the introduction of a fast statistical algorithm for intermediate state averaging makes the method promising also for computing nonlinear response functions. With the use of random vector averaging for the intermediate states, the task of evaluating the multi-dimensional time integral is reduced to calculating a number of one-dimensional integrals. Then the CPU time necessary for computing a nonlinear response function scales only linearly both with the number of basis states and with the inverse of the required energy resolution, irrespective of the order of nonlinearity. The effectiveness of the algorithm is demonstrated in the calculation of the TPA spectra of silicon. We discuss future applications in such areas as the investigation of electronic properties of biomolecules and complex systems, and designing materials of large nonlinear optical properties.

Fast Algorithm for Calculating Two-Photon Absorption Spectra by Real-Time Real-Space Higher-Order Finite-Difference Method

The newly developed fast algorithm for the calculation of nonlinear response functions is applied to the calculation of the two-photon absorption spectra of crystalline silicon. The algorithm combines the real-time real-space higher-order finite-difference method with the use of random vectors for intermediate states. Despite the radical difference in methodology, the result is in fair agreement with that of the conventional method.

Coulomb scattering of excited carriers within RPA; calculation in real time domain

Abstract We have carried out a large-scale simulation of transient behavior of hot carriers in semiconductors excited by ultrashort laser pulses treating Coulomb interaction to high orders within the framework of random phase approximation (RPA). We have used the non-equilibrium Greens function method with the explicit dependence on two time variables and integrated the Dysons equation numerically in the time domain on the large-scale parallel computer. We examine the dynamics of Coulomb screening by comparing the time development of polarization and the photon echo signal under two types of approximation to Coulomb interaction effects, i.e., RPA and HF (Hartree–Fock approximation).