arXiv subjects

Yoshiaki Sato

Publications and source records attributed to Yoshiaki Sato.

7 recordsLinked to original sources

arXiv2026

Numerical Investigation of Efficient Electron Acceleration at an Unsteady Solar Flare Loop-Top

Using magnetohydrodynamic (MHD) fields and guiding-center test-particle calculations, this study investigates how time-dependent loop-top dynamics modulate the adiabatic energization of electrons in a solar flare. Our results indicate that a time-varying loop-top structure enhances acceleration efficiency compared to a quasi-steady one. In the quasi-steady velocity field, the net acceleration is suppressed due to the decelerating effect of betatron cooling. Conversely, in the unsteady velocity field, the betatron mechanism readily accelerates electrons within the compressed magnetic field at the edge of the loop-top. These findings suggest that the acceleration of electrons at the loop-top is driven not only by the static shape of the magnetic structure but also by dynamic events such as plasmoid collisions. While previous studies have primarily focused on acceleration processes within the reconnection outflow, such as at termination shocks or within plasmoids, our research highlights the importance of the acceleration and deceleration processes at the exit point where electrons escape from the loop-top.

astro-ph.SR↗

arXiv2025

Enabling Technologies for Scalable Superconducting Quantum Computing

Experiments with superconducting quantum processors have successfully demonstrated the basic functions needed for quantum computation and evidence of utility, albeit without a sizable array of error-corrected qubits. The realization of the full potential of quantum computing centers on achieving large scale fault-tolerant quantum computers. Science, engineering and industry advances are needed to robustly generate, sustain, and efficiently manipulate an exponentially large computational (Hilbert) space as well as supply the number and quality components needed for such a scaled system. In this article, we suggest critical areas of quantum system and ecosystem development, with respect to the handling and transmission of quantum information within and out of a cryogenic environment, that would accelerate the development of quantum computers based on superconducting circuits.

quant-ph↗

arXiv2022

Precise magnetization measurements down to 500 mK using a miniature 3He cryostat and a closed-cycle 3He gas handling system installed in a SQUID magnetometer without continuous-cooling functionality

We have conducted precise magnetization measurements down to 0.5 K with a miniature 3He cryostat and a closed-cycle 3He gas handling system for a commercial superconducting quantum interference device magnetometer [Magnetic Property Measurement System (Quantum Design)]. The gas handling system contains two sorption pumps filled with granular charcoals. We pressurize 3He gas up to ambient pressure for the liquification at 3 K and then pump the vaper for cooling. The lowest sample temperature is ~ 0.5 K and it can persist for 34 hours. We demonstrate the performance of the system by observing the Meissner effect of aluminum below the superconducting transition temperature ~ 1 K. We also measured the magnetization curve of the heavy fermion superconductor CeCoIn5 resulting in successful observation of the lower critical field at 0.5 K.

cond-mat.supr-con↗

arXiv2017

Different metamagnetism between paramagnetic Ce and Yb isomorphs

To solve the puzzle of metamagnetic phenomena in heavy fermion systems, we have compared paramagnetic isostructural Ce and Yb systems, CeNi$_2$Ge$_2$ and YbNi$_2$Ge$_2$, both of which are located near a magnetic instability. The most intriguing result is discovery of a metamagnetic-like transition in both systems from magnetization measurements in a pulsed magnetic fields. This is the first observation of the metamagnetism for isomorphic Ce and Yb paramagnetic systems. Similar to other metamagnets, the metamagnetic transition fields for both compounds are well scaled by the temperature $T_χ^{\rm max}$, at which the magnetic susceptibility shows a maximum. In addition, for CeNi$_2$Ge$_2$ a peak of nonlinear susceptibility $χ_3$ appears at approximately $T_χ^{\rm max}/2$, as for other heavy-fermion metamagnets. In contrast, YbNi$_2$Ge$_2$ shows only a sign change for $χ_3$ at $T_χ^{\rm max}$, as observed in itinerant metamagnets located near the ferromagnetic critical point. The metamagnetism of CeNi$_2$Ge$_2$ corresponds to a typical Kondo lattice system, whereas that of YbNi$_2$Ge$_2$ is similar to the nearly ferromagnetic itinerant systems. Other possibilities for the metamagnetic behavior of YbNi$_2$Ge$_2$ are also discussed.

cond-mat.str-el↗

arXiv2017

Critical Behavior in Doping-Driven Metal$-$Insulator Transition on Single-Crystalline Organic Mott-FET

We present the carrier transport properties in the vicinity of a doping-driven Mott transition observed at a field-effect transistor (FET) channel using a single crystal of the typical two-dimensional organic Mott insulator $κ$-(BEDT-TTF)$_2$CuN(CN)$_2$Cl ($κ$-Cl).The FET shows a continuous metal$-$insulator transition (MIT) as electrostatic doping proceeds. The phase transition appears to involve two-step crossovers, one in Hall measurement and the other in conductivity measurement. The crossover in conductivity occurs around the conductance quantum $e^2/h$ , and hence is not associated with "bad metal" behavior, which is in stark contrast to the MIT in half-filled organic Mott insulators or that in doped inorganic Mott insulators. Through in-depth scaling analysis of the conductivity, it is found that the above carrier transport properties in the vicinity of the MIT can be described by a high-temperature Mott quantum critical crossover, which is theoretically argued to be a ubiquitous feature of various types of Mott transitions. [This document is the unedited Authors' version of a Submitted Work that was subsequently accepted for publication in Nano Letters, copyright ©American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/acs.nanolett.6b03817]

cond-mat.str-el↗

arXiv2016

Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator

It is widely recognised that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high $T_{\rm c}$ cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting Fermi surface under electron doping.

cond-mat.str-el↗

arXiv2011

Electrically Controlled Adsorption of Oxygen in Bilayer Graphene Devices

We investigate the chemisorptions of oxygen molecules on bilayer graphene (BLG) and its electrically modified charge-doping effect using conductivity measurement of the field effect transistor channeled with BLG. We demonstrate that the change of the Fermi level by manipulating the gate electric field significantly affects not only the rate of molecular adsorption but also the carrier-scattering strength of adsorbed molecules. Exploration of the charge transfer kinetics reveals the electrochemical nature of the oxygen adsorption on BLG. [This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, © American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/nl202002p.]

cond-mat.mes-hall↗