Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Harada Yuichi Last modified date:2019.08.30

Professor / Global Innovation Center / Global Innovation Center

1. Hiroshi Irie, Clements Todt, Norio Kumada, Harada, Yuichi, Hiroki Sugiyama, Tatsushi Akazaki, Koji Muraki, Andreev reflection and bound state formation in a ballistic two-dimensional electron gas probed by a quantum point contact, Physical Review B, 10.1103/PhysRevB.94.155305, 94, 155305-6, 2016.10, We study coherent transport and bound state formation of Bogoliubov quasiparticles in a high-mobility In0.75Ga0.25As two-dimensional electron gas (2DEG) coupled to a superconducting Nb electrode by means of a quantum point contact (QPC) as a tunable single-mode probe. Below the superconducting critical temperature of Nb, the QPC shows a single-channel conductance greater than the conductance quantum 2e2/h at zero bias, which indicates the presence of Andreev-reflected quasiparticles, time-reversed states of the injected electron, returning back through the QPC. The marked sensitivity of the conductance enhancement to voltage bias and perpendicular magnetic field suggests a mechanism analogous to reflectionless tunneling—a hallmark of phase-coherent transport, with the boundary of the 2DEG cavity playing the role of scatterers. When the QPC transmission is reduced to the tunneling regime, the differential conductance vs bias voltage probes the single-particle density of states in the proximity area. Measured conductance spectra show a double peak within the superconducting gap of Nb, demonstrating the formation of Andreev bound states in the 2DEG. Both of these results, obtained in the open and closed geometries, underpin the coherent nature of quasiparticles, i.e., phase-coherent Andreev reflection at the InGaAs/Nb interface and coherent propagation in the ballistic 2DEG..
2. Harada, Yuichi, Nanowire-nanoantenna coupled system fabricated by nanomanipulation, OPTICS EXPRESS, 10.1364/OE.24.008647, 24, 8, 8647-8659, 2016.04.
3. Harada, Yuichi, Detection of Coherent Terahertz Radiation from a High-Temperature Superconductor Josephson Junction by a Semiconductor Quantum-Dot Detector, PHYSICAL REVIEW APPLIED, 10.1103/PhysRevApplied.5.024010, 5, 2, 2016.02.
4. Harada, Yuichi, Gate-controlled semimetal-topological insulator transition in an InAs/GaSb heterostructure, PHYSICAL REVIEW B, 10.1103/PhysRevB.91.245309, 91, 24, 2015.06.
5. Harada, Yuichi, Self-aligned gate-all-around InAs/InP core-shell nanowire field-effect transistors, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.7567/JJAP.54.04DN04, 54, 4, 2015.04.
6. Harada, Yuichi, Iriel, Hiroshi, Sugiyama, Hiroki, Akazaki, Tatsushi, Josephson coupling through one-dimensional ballistic channel in semiconductor-superconductor hybrid quantum point contacts, PHYSICAL REVIEW B, 10.1103/PhysRevB.89.165415, 89, 16, 2014.04, We study a superconducting quantum point contact made of a narrow In0.75Ga0.25As channel with Nb proximity electrodes. The narrow channel is formed in a gate-fitted constriction of InGaAs/InAlAs/InP heterostructure hosting a two-dimensional electron gas.When the channel opening is varied with the gate, the Josephson critical current exhibits a discretized variation that arises from the quantization of the transverse momentum in the channel. The quantization of Josephson critical current persists down to the single-channel regime, providing an unambiguous demonstration of a semiconductor-superconductor hybrid Josephson junction involving only a single ballistic channel..
7. Yuichi Harada, N. Hirose, Y. Uzawa, M. Sekine, Characteristics of all-Nb thin film microbridges by nanometer fabrication, 23rd International Conference on Solid State Devices and Materials - SSDM '91 Conference on Solid State Devices and Materials, 520-522, 1991, We have fabricated the all-Nb thin film microbridges by our developed nanometer process. These microbridges have high sensitivity of radiation and reliability. It is observed that the properties of devices change by varying the sizes of bridge-region. We have also fabricated the series arrays and observed that they operate coherently..
8. Nobumitsu Hirose, Yuichi Harada, Shigeru Yoshimori, Mitsuo Kawamura, FABRICATION OF SELF-ALIGNMENT MICRO-CONTACT JOSEPHSON JUNCTIONS., Transactions of the Institute of Electronics and Communication Engineers of Japan. Section E, E69, 4, 425-426, 1986.04, We fabricated micro-contact Josephson junctions by self-alignment process, using double-layer-resist electron beam exposure and RIE. We chose NB as superconductive materials. The junctions show the Josephson effect under millimeter wave (70 GHz) radiation less than 100 mu w and the 7th Shapiro step..
9. Yuichi Harada, Nobumitsu Hirose, Yoshinori Uzawa, Properties of the nb thin-film nanobridges prepared by nanometer fabrication process, Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes, 10.1143/JJAP.30.3933, 30, 12, 3933-3937, 1991, We describe the properties of Nb thin-film nanobridges fabricated by means of our original nanometer-scale process. Our original nanofabrication techniques include the synthesis of a new electron beam (EB) resist and the use of CBrF3 as an etchant for reactive ion etching (RIE). Fabricated nanobridges have high sensitivity of radiation and high reliability. It is observed that the properties of nanobridges can be changed by varying the bridge length and its thickness. We have also fabricated the series arrays and observed that they operate coherently..