Kyushu University [Harada Yuichi (Professor) Academic Research and Industrial Collaboration Management Office of Kyushu University, ]

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Harada Yuichi
Professor
Academic Research and Industrial Collaboration Management Office of Kyushu University
Last modified date：2023.11.27

Graduate School

Department of Interdisciplinary Engineering Sciences
Interdisciplinary Graduate School of Engineering Sciences

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Academic Research and Industrial Collaboration Management Office of Kyushu University
Integrated Initiative for Designing Future Society
Open Innovation Platform
Kyushu University Platform of Inter/Transdisciplinary Energy Research
Robert T.Huang Entreprenuership Center of Kyushu University(QREC)
Global Innovation Center

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Country of degree conferring institution (Overseas)

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Total Priod of education and research career in the foreign country

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1.	Sameh Okashaa, Yoshiaki Sekine, Satoshi Sasaki, Yuichi Haradaa, Atomic layer deposition of aluminum (111) thin film by dimethylethylaminealane precursor, Thin Solid Films, https://doi.org/10.1016/j.tsf.2021.138784, 732, 138784, 2021.06, We report the growth of aluminum (111) thin film by atomic layer deposition (ALD) technique with dimethy- lethylaminealane (DMEAA) as a precursor. It is found that the metallic underlayer is essential to grow uniform aluminum films by DMEAA precursor. As a titanium thin film is used as the underlayer, grown aluminum thin film shows (111) orientation irrespective of substrates. The lattice constant and superconducting transition temperature of the aluminum thin films are the same as the bulk one. These findings suggest that ALD technique provides high quality of the aluminum thin films and have potential for the applications of superconducting devices. We discuss ALD technique with DMEAA precursor is the promising method for fabricating vertical small Josephson tunnel junctions, which can be used as the superconducting quantum bits..
2.	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..
3.	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..