Showing papers by "Hideaki Takayanagi published in 2000"
TL;DR: In this paper, the incoherent regime of multiple Andreev reflections (MAR) is studied in long diffusive SNS junctions at applied voltages larger than the Thouless energy.
Abstract: The incoherent regime of multiple Andreev reflections (MAR) is studied in long diffusive SNS junctions at applied voltages larger than the Thouless energy. Incoherent MAR are treated as a transport problem in energy space by means of a circuit theory for an equivalent electrical network. The current through NS interfaces is explained in terms of diffusion flows of electrons and holes through ``tunnel'' and ``Andreev'' resistors. These resistors in diffusive junctions play roles analogous to the normal and Andreev reflection coefficients in Octavio-Tinkham-Blonder-Klapwijk theory for ballistic junctions. The theory is applied to the subharmonic gap structure (SGS); simple analytical results are obtained for the distribution function and current spectral density for the limiting cases of resistive and transparent NS interfaces. In the general case, the exact solution is found in terms of chain fractions, and the current is calculated numerically. SGS shows qualitatively different behavior for even and odd subharmonic numbers $n=2\ensuremath{\Delta}/eV,$ and the maximum slopes of the differential resistance correspond to the gap subharmonics, $eV=2\ensuremath{\Delta}/n.$ The influence of inelastic scattering on the subgap anomalies of the differential resistance is analyzed.
46 citations
TL;DR: In this article, a mesoscopic cross-like normal-metal structure connected to two superconducting (S) and two normal (N) reservoirs was studied and the Josephson effect was observed under unusual conditions when there was no current through one of the two S/N interfaces.
Abstract: We studied a mesoscopic crosslike normal-metal structure connected to two superconducting (S) and two normal (N) reservoirs. We observed the Josephson effect under unusual conditions when there is no current through one of the two S/N interfaces. The potential difference between the S reservoirs was zero unless the voltage applied between S and N reservoirs exceeded a critical value although the electric potential in the N wire connecting the superconductors varied in a nonmonotonic way. The observed effects are discussed theoretically.
26 citations
TL;DR: In this paper, the authors investigated the fluxon dynamics in isolated long Josephson junctions and found that the fluxons obey a double sine-Gordon (DSG) equation based on the change in the Josephson acceleration relation, i.e., the voltage-phase difference relation.
Abstract: A quantum flux, a 2π fluxon, described by a sine-Gordon equation is an elementary excitation in long Josephson junctions. We investigated the fluxon dynamics in isolated long Josephson junctions. In such isolated systems, the total number of Cooper pairs is conserved, so the fluxon dynamics may change. We found that the fluxons obey a double sine-Gordon (DSG) equation based on this change in the Josephson acceleration relation, i.e., the voltage-phase difference relation. It should be possible to confirm the existence of DSG fluxons by detecting the relative oscillations of two π fluxons.
14 citations
TL;DR: In this article, the gate voltage dependence of the spin-orbit coupling parameter α was analyzed by analyzing the gatevoltage-dependent beating pattern observed in the Shubnikov-de Haas oscillation.
Abstract: A gated inverted In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well is studied via magneto transport. By analysing the gate-voltage-dependent beating pattern observed in the Shubnikov-de Haas oscillation, we determine the gate voltage (or electron concentration) dependence of the spin-orbit coupling parameter α. Our experimental data and their analysis show that the band nonparbolicity effect cannot be neglected. For electron concentrations above 2×10 12 cm −2 , it causes a reduction of α up to 25%. We report for the first time the α value for the second subband.
13 citations
TL;DR: In this article, the gate voltage-dependent Aharonov-Bohm oscillations in an InGaAs-based two-dimensional electron gas ring with a gate on top of one of the branches were measured.
Abstract: We measured gate voltage-dependent Aharonov–Bohm oscillations in an InGaAs-based two-dimensional electron gas ring with a gate on top of one of the branches. After ensemble averaging, the h/e oscillation spectrum showed smooth oscillatory behavior as a function of the gate voltage. This could be a manifestation of the spin–orbit interaction induced interference.
11 citations
TL;DR: In this article, two types of bipartite semiconductor-dot arrays are proposed, which exhibit flat band characteristics and are theoretically predicted to have ferromagnetic properties, although they do not contain any magnetic elements.
Abstract: Ferromagnetism in semiconductor-dot arrays is theoretically predicted. The two types of bipartite semiconductor-dot arrays which we propose exhibit flat band characteristics. According to the Lieb theorem, ferromagnetism is predicted, although our designed dot arrays do not contain any magnetic elements. We also investigate the typical dot-radius and inter-dot distance for the realization of the semiconductor-dot ferromagnetism, and several applications are discussed.
11 citations
Patent•
08 Dec 2000TL;DR: In this article, a practically realizable semiconductor magnetic body having a flat-band structure is disclosed. But the structure of the semiconductor body is not described in detail, except that it is formed by semiconductor quantum dots arranged on lattice points such that electrons can transfer between neighboring quantum dots and the electron energy band contains a flatband structure.
Abstract: A practically realizable semiconductor magnetic body having a flat-band structure is disclosed. The semiconductor magnetic body is formed by semiconductor quantum dots arranged on lattice points such that electrons can transfer between neighboring quantum dots and the electron energy band contains a flat-band structure, where each quantum dot is a structure in which electrons are confined inside a region which is surrounded by high energy potential regions, and the flat-band structure is a band structure in which energy dispersion of electrons has hardly any wave number dependency.
9 citations
4 citations
TL;DR: In this article, the authors investigated giant Andreev backscattering (GAB) in a superconductor (S)-semiconductor two-dimensional electron gas (2DEG) junction with a special gate configuration.
Abstract: We investigated giant Andreev backscattering (GAB) in a superconductor (S)-semiconductor two-dimensional electron gas (2DEG) junction with a special gate configuration: a split gate which produces ...
4 citations
Patent•
08 Dec 2000
TL;DR: In this article, the flat-band structure of semiconductor quantum stream is used to provide a semiconductor magnetic substance, having a flatband structure by forming a quantum stream, while using semiconductor manufacturing technology and growing technology.
Abstract: PROBLEM TO BE SOLVED: To provide a semiconductor magnetic substance, having a flat-band structure by forming a quantum stream, while using semiconductor manufacturing technology and growing technology. SOLUTION: This magnetic substance is formed by making electrons movable between adjacent quantum dots and including the flat-band structure, in which energy diffusion of electrons hardly depends on wave number, in an electron energy band by locating the semiconductor quantum dots, with which the area of high energy potential is formed around the periphery and the electrons are contained, on grid points.
3 citations
TL;DR: In this paper, the phase of magnetoconductance oscillations can switch between 0 and π depending on the resistance of intermetallic interfaces and temperature, and the effect is due to a nontrivial interplay between the proximityinduced enhancement of the local conductivity and the proximity-induced suppression of the density of states at low energies.
Abstract: Interference of proximity-induced superconducting correlations in mesoscopic metallic rings is sensitive to the magnetic flux Φ inside these rings. This is the reason for magnetoconductance oscillations in such systems. We detected experimentally and explained theoretically a novel effect: the phase of these oscillations can switch between 0 and π depending on the resistance of intermetallic interfaces and temperature. The effect is due to a nontrivial interplay between the proximity-induced enhancement of the local conductivity and the proximity-induced suppression of the density of states at low energies.
TL;DR: In this article, the superconducting proximity correction modifies the average conductance of the wire eventhough the latter gives a mesoscopic fluctuation, and the charging effect is depicted by a gate control of thesuperconducting island.
Abstract: We theoretically investigated superconducting proximitycorrections of the conductance of a mesoscopic metal wire interms of the Kubo-formula. In diagrammatic expression, theelectromagnetic response kernel is quite similar to that ofreproducible conductance fluctuation. However, the proximitycorrection modifies the average conductance of the wire eventhough the latter gives a mesoscopic fluctuation.This Kubo-formula expression is applicable to the analysis ofcharging effects on the proximity correction in asuperconductor(S)/Mesoscopic-normalmetal-wire(N) hybrid systemwith a very small S/N interface. Although the chargingeffect exponentially suppresses Andreev reflections at theS/N interface, the proximity correction survives.We propose an experiment to confirm this charging effect,where a degenerated semiconductor is used as the normal-metalwire. The proximity correction can be picked from the entireconductance as the magnetoconductance of an interferometer,and the charging effect is depicted by a gate control of thesuperconducting island. The semiconductor interferometer ismore promising than a metallic one because the conductancewithout the proximity effect is bigger.
TL;DR: In this paper, the authors investigated giant Andreev backscattering in a superconductor (S) junction with two kinds of gate: a quantum point contact (QPC) and an ordinary wide gate.
Abstract: We investigated giant Andreev backscattering in a superconductor (S) – two-dimensional electron gas (2DEG) junction with two kinds of gate: a quantum point contact (QPC) and an ordinary wide gate. Though the diffusive 2DEG itself displayed reentrant conductance, by attaching a QPC we observed conductance enhancement (peak) at zero energy. The bias voltage and the magnetic field dependence of the enhancement at different degrees of dirtiness showed that phase conjugation between an electron and a hole is essential for enhancement.
TL;DR: In this paper, a phenomenological model for dissipative dynamics of a superfluid was proposed, and the results of the experiment on a helium three weak link system gave strong support for their model.
Abstract: We propose a simple phenomenological model for dissipative dynamics of a superfluid. Qualitative agreement between the results of our numerical calculations and of the experiment on a superfluid helium three weak link system gives strong support for our model.
TL;DR: In this article, the in-plane magneto-transport properties of a 2DEG in an InAs inserted InGaAs/InAlAs heterostructure with a DC bias voltage were investigated.
Abstract: We report studies of the in-plane magneto-transport properties of a 2DEG in an InAs inserted InGaAs/InAlAs heterostructure with a DC bias voltage. Temperature dependent zero-bias reduction of the longitudinal resistance was observed when high magnetic field is applied along the sample growth direction. We interpret the observed resistance reduction as the result of a Coulomb gap existing at the Fermi level of the 2DEG.