Showing papers by "Saburo Takahashi published in 2002"

Design of vertical breakwaters

Abstract: In this book, different types of breakwaters are introduced and their historical development is described in order to understand the advantages and disadvantages associated with each type of breakwater. The failures of breakwaters are then discussed to demonstrate crucial points in their stability design. Finally, the design methods used for vertical are explained including a new design concept of performance design for vertical breakwaters. Since the design methodology for rubble mound breakwaters has been addressed in many textbooks, the design of vertical breakwaters will be concentrated on here.

Hall effect induced by a spin-polarized current in superconductors.

Abstract: We propose a novel anomalous Hall effect caused by the spin-polarized current in superconductors (SC). The spin-polarized quasiparticles flowing in SC are deflected by spin-orbit scattering to yield a quasiparticle charge imbalance in the transverse direction. Overall charge neutrality gives rise to a compensating change in the number of Cooper pairs. A transverse electric field builds up as opposed to an acceleration of the Cooper pairs, producing the Hall voltage. It is found that the Hall voltages due to the side jump and skew scattering mechanisms have different temperature dependence in the superconducting state. A spin-injection Hall device to generate the ac Josephson effect is proposed.

Spin transport and relaxation in superconductors

Abstract: We study theoretically the effect of spin relaxation on the spin transport in a ferromagnet/superconductor (FM/SC) tunnel junction. When spin-polarized electrons are injected into the SC from the FM, nonequilibrium spin accumulation as well as spin current are created in the range of the spin diffusion length in the SC. We find that the spin diffusion length in the superconducting state is the same as that in the normal state. We examine a FM/SC/SC double tunnel junction, and show that the spin current is detected by the Joule heat generated at the Josephson junction. This provides a method to obtain the spin diffusion length by probing the spin current in SC's.

Spin injection element and magnetic apparatus using the same

Abstract: PROBLEM TO BE SOLVED: To provide a magnetic apparatus using a spin injection element which can provide a large signal voltage with a low current and a low magnetic field and can also be micronized. SOLUTION: A first and a second tunnel junctions (2, 3), wherein a non-magnetic conductor 4 is used as a common electrode while ferroelectric materials (6, 8) are used as the electrode, are arranged with an interval which is shorter than the spin spreading length of the non-magnetic conductor 4. Moreover, in the first tunnel junction 2, the spin is injected to the non-magnetic conductor 4 from a ferroelectric metal 6. In the second tunnel junction 3, a voltage accompanying the spin injection of the first tunnel junction 2 is detected between the ferroelectric material 8 and non-magnetic conductor 4. The non-magnetic conductor 4 is lower then the metal in the carrier density. A large signal voltage can be obtained with a low current and a low magnetic field. A high sensitivity magnetic sensor, a high sensitivity magnetic head, and MRAM having a large signal voltage can be provided by using such non-magnetic conductor as a magnetic device. COPYRIGHT: (C)2004,JPO&NCIPI

Spin injection into superconductors

Abstract: It is shown that when a spin-polarized current is injected into a superconductor from a ferromagnet in ferromagnet/superconductor (FM/SC) and FM/SC/FM tunnel junctions, the spin and charge degrees of freedom of electrons are carried by quasi-particles and Cooper pairs in SC, respectively. The spin accumulation competes with the superconductivity and the spin current gives rise to the transverse charge current in SC.

Andreev reflection in narrow ferromagnet/superconductor point contacts

Abstract: We theoretically study the conductance quantization and Andreev reflection of narrow ferromagnet/superconductor point contacts. The conductance quantization is shown to depend on whether the contact region is superconducting or ferromagnetic as well as on the strength of the exchange field in the ferromagnet. The Andreev reflection is more suppressed than that of the superconducting contact. We also find that the conductance–voltage curve shows a bump at zero bias voltage if there is no interfacial scattering. On the contrary, the conductance–voltage curve shows a dip if the contact has an interfacial scattering.