ISSP - The institute for Solid State Physics

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Professor

Shingo
KATSUMOTO

Research Associate

Taketomo
NAKAMURA

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With the techniques of epitaxial growth of high quality semiconductor films, vacuum depositions of metallic films, and lithography from micron to a few tens of nanometers, we prepare low dimensional systems such as quantum wells, wires and dots and quantum circuits composed of them to study the quantum many body effects. Our research interests also go to some applications of the physics of electron and nuclear spins to so called spintronics, and quantum information manipulation, classical logic devices with the use of superconductivity. One of our present primary subjects is the creation of spin currents in non-magnetic semiconductor quantum structures with electric currents and the spin-orbit interaction and the detection of the resultant spin polarization with a side-coupled quantum dots. Another is the spin injection from ferromagnets into semiconductors via almost localized states in quantum dots. We are also studying the physics of the Andreev bound states appear at boundaries between semiconductor naonwires with strong spin-orbit interaction and superconductors.

(a) Electron beam micrograph of a device to detect spin polarization in a quantum point contact (QPC). (b) Green-white-red image plot of the QPC conductance variation as a function of the plunger gate voltage of the detector quantum dot (QD) and the amplitude of the square wave superposed. The numbers indicate the number of electrons in the QD and the vertical arrows indicate excited states.

Conductance of an InAs quantum wire through Andreev bound states (ABSs) as a function of source-drain voltage. The inset shows the device structure. The oscillation due to the resonance between the ABSs and the AC Josephson effect is largely diminished with the spin Hall effect caused by the current through the InAs quantum wire.