We investigate the electronic transport characteristics of a one-dimensional ͑1D͒ narrow constriction defined in a GaAs/ Al x Ga 1−x As heterostructure by a simple triple-gate structure consisting of a pair of split gates and an additional surface Schottky gate ͑center gate͒ between them. Comparison between devices with and without a center gate reveals that the center gate, even when zero biased ͑V CG =0 V͒, significantly modifies the surface potential and facilitates the 1D confinement in a deep two-dimensional electron system. The pinch-off voltages at V CG = 0 V for various channel widths W ͑=0.4-0.8 m͒ and lengths L ͑=0.2-2 m͒ are well described by the analytical formula based on the pinned-surface model ͓J. H. Davies et al., J. Appl. Phys. 77, 4504 ͑1995͔͒. Nonlinear transport spectroscopy with an additional dc bias shows that the lowest 1D subband energy separation ͑⌬E 1,2 ͒ changes linearly with V CG and can be enhanced by 70% for V CG = 0.8 V. A simple model assuming an infinitely long channel and no self-consistent potential well reproduces the overall behavior of the measured ⌬E 1,2. In addition, effects of impurities, occasionally found for long-channel devices ͑L ജ 1 m͒, are found to be greatly reduced by applying positive V CG and thereby enhancing ⌬E 1,2. Data are also presented for the transport anomaly below the first conductance plateau, the so-called "0.7 anomaly," demonstrating that the triple-gate structure is useful for the study of density-dependent phenomena in a 1D system.
Transmission characteristics at visible light range in a one-dimensional superconductor-dielectric photonic crystal have been numerically analyzed based on the finite element method using COMSOL RF module. The two-fluid model and wavelength-dependent dispersion formula were adopted to describe the optical response of the low temperature superconducting system. The simulation results clearly reveal a cutoff frequency or a photonic band gap that can be manipulated through the thicknesses of the superconductor and dielectric layers as well as the ambient temperature of the system. It is observed that the shift of cutoff frequency becomes more noticeable by adjusting the thickness of the superconductor layer than that of the dielectric one. Furthermore, the cutoff frequency becomes very sensitive when the system temperature is tuned to close vicinity of the critical temperature of the superconductor.
This paper reviews the progress made over the last few years in understanding the development of perpendicular magnetic tunneling junctions (pMTJs). The material systems for making pMTJs, including rare-earth/transition metal alloys, L10-ordered (Co, Fe)–Pt alloys, Co/(Pd, Pt) multilayers, and CoFeB–MgO crystallized structures, are briefly introduced. The fabrication processes of the MTJ devices are focused on, consisting of open-trench, etch-back and self-aligned techniques. The authors also propose a spin-torque nano-oscillator based on pMTJ, for application in GHz range telecommunications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.