arXiv subjects

Daisuke Matsubayashi

Publications and source records attributed to Daisuke Matsubayashi.

3 recordsLinked to original sources

arXiv2025

The impact of process steps on nearly ideal subthreshold slope in 300-mm compatible InGaZnO TFT

While we demonstrate a back-gated (BG) amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) transistors with a nearly ideal subthreshold slope (SS) ~ 60 mV/dec. However, SS degrades when a top-gated (TG) configuration is implemented. The energy distribution of traps inferred from temperature-dependent (T = 4 K - 300 K) and multi-frequency (f = 1 kHz - 100 kHz) admittance measurements, reveals a much higher trap density in TG devices. By analyzing the impact of each process step and conducting forming gas anneal (FGA) experiments, we reveal the role of hydrogen in the deterioration of the SS in the IGZO-based transistors.

physics.app-ph↗

arXiv2009

Numerical Study of Current-Induced Domain-Wall Dynamics: Crossover from Spin Transfer to Momentum Transfer

We study current-induced dynamics of a magnetic domain wall by solving a time-dependent Schrödinger equation combined with Landau-Lifshitz-Gilbert equation in a one-dimensional electron system coupled to localized spins. Two types of domain-wall motions are observed depending on the hard-axis anisotropy, $K_{\perp}$, of the localized spin system. For small values of $K_{\perp}$, the magnetic domain wall shows a streaming motion driven by spin transfer. In contrast, for large values of $K_{\perp}$, a stick-slip motion driven by momentum transfer is obtained. We clarify the origin of these characters of domain-wall motions in terms of the dynamics of one-particle energy levels and distribution functions.

cond-mat.mes-hall↗

arXiv2007

Spin splitting and Kondo effect in quantum dots coupled to noncollinear ferromagnetic leads

We study the Kondo effect in a quantum dot coupled to two noncollinear ferromagnetic leads. First, we study the spin splitting $δε=ε_{\downarrow}-ε_{\uparrow}$ of an energy level in the quantum dot by tunnel couplings to the ferromagnetic leads, using the Poor man's scaling method. The spin splitting takes place in an intermediate direction between magnetic moments in the two leads. $δε\propto p\sqrt{\cos^2(θ/2)+v^2\sin^2(θ/2)}$, where $p$ is the spin polarization in the leads, $θ$ is the angle between the magnetic moments, and $v$ is an asymmetric factor of tunnel barriers ($-1<v<1$). Hence the spin splitting is always maximal in the parallel alignment of two ferromagnets ($θ=0$) and minimal in the antiparallel alignment ($θ=π$). Second, we calculate the Kondo temperature $T_{\mathrm{K}}$. The scaling calculation yields an analytical expression of $T_{\mathrm{K}}$ as a function of $θ$ and $p$, $T_{\mathrm{K}}(θ, p)$, when $δε\ll T_{\mathrm{K}}$. $T_{\mathrm{K}}(θ, p)$ is a decreasing function with respect to $p\sqrt{\cos^2(θ/2)+v^2\sin^2(θ/2)}$. When $δε$ is relevant, we evaluate $T_{\mathrm{K}}(δε, θ, p)$ using the slave-boson mean-field theory. The Kondo resonance is split into two by finite $δε$, which results in the spin accumulation in the quantum dot and suppression of the Kondo effect.

cond-mat.mes-hall↗