Quantum Device Laboratory

A. Nakayama

Akiyoshi Nakayama
(Professor)

Office: 23-707 Ext.: 3835

e-mail: nakayama@ee.kanagawa-u.ac.jp

03/1985, Ph.D., The University of Tokyo

03/1983, M.S., The University of Tokyo

N. Watanabe

Norimichi Watanabe
(Assistant professor)

Laboratory: 23-602 Ext.: 3791

e-mail: ft102002ho@kanagawa-u.ac.jp

03/2007, Ph.D., Kanagawa University

Research Field

Superconducting Devices, Applications of Magnetic Materials, Magnetic Sensors.

Research Overview

Fabricating thin films of niobium and aluminum by DC sputtering. Measuring the electrical and magnetic properties of quantum devices.

Research Subjects

  • 1.Josephson tunnel junctions.
  • 2.Superconducting circuits.

Introduction:

Josephson current can flow between two superconducting electrodes of a tunnel junction without voltage drop. To fabricate superconducting niobium tunnel junctions, niobium and aluminum thin films were deposited in separate vacuum chambers by a DC magnetron sputtering vacuum system with a load-lock chamber. The tunnel oxide of niobium/aluminum-oxide /niobium tunnel junctions was formed by natural oxidation of the surface of the aluminum film in a pure oxygen atmosphere. The junction areas were defined by a selective niobium anodization process.
The junction size was 50 micrometer square. To obtain the magnetic field dependence, the external magnetic field for the junction was produced by three pairs of Helmholtz coils (Fig. 1). Two pairs of Helmholtz coils produced magnetic fields, Hx and Hy, parallel to the junction plane and the third pair produced a magnetic field, Hz, perpendicular to the junction plane.

The maximum fields that Helmholtz coils produced, were 3000 A/m for Hx and Hy, and 8000 A/m for vertical field Hz. The Helmholtz coils were driven by using a DC power supply and controlled by personal computer and general purpose interface bus system.

Publications
  • 1) A.Nakayama, S.Abe, N.Watanabe, “Deviation From Fraunhofer-Type Modulation of Josephson Current Through Niobium Tunnel Junctions by Applying Vertical Magnetic Field” IEEE Trans. Appl. Supercond, 26, 1100606 (2016).
  • 2) A.Nakayama, S.Abe, Y.Nishi, N.Watanabe, Y.Okabe “Two-dimensional magnetic field dependence of zero and finite voltage steps in current-voltage characteristics of superconducting quantum interference devices” Microelectron. Eng, 146, 19(2015).
  • 3) N.Watanabe, S.Abe, A.Nakayama “Modulation of a Josephson current through an Nb/Al-AlOx/Nb Josephson junction by a parallel magnetic field and a perpendicular magnetic field” J. Appl. Phys, 116, 033920 (2014).
Affiliated Academic Organizations

A. Nakayama: The Institute of Electronics, Information and Communication Engineers (IEICE), The Japan Society of Applied Physics.

N. Watanabe: The Institute of Electronics, Information and Communication Engineers (IEICE), The Japan Society of Applied Physics, The Magnetics Society of Japan, The Japan Institute of Metals and Materials.

Current members
◯ Professors: 1 ◯ Assistant Professors: 1
◯ Postgraduates: 1 ◯ Undergraduates: 16

Facilities: DC magnetron sputtering system, system for measuring 3D magnetic field dependence of Josephson current.

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