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Research summary 2007

We study prominent quantum phenomena in condensed matter in a wide temperature range including micro Kelvin region. We carried out the experiment on surface phenomena of superfluid 3He. The surface of rotating superfluid 4He was studied. Millimeter wave absorption induced resistance of surface sate elecrons on liquid He is systematically measuredand extension to lower temperatures was carried out, where ripplon scattering is important. A vertical double quantum dots based on GaAs semiconductor was fabricated and transport properties under high magnetic fields and light irradiation have been studied.

Surface phenomena on quantum systems

  1. The excitation of surface state electrons by irradiating 130GHz millimeter wave induces a prominent resistivityincrease. The observed effect is interpreted as a clear evidence for the realization of ultrahot electons. Measurement was extended to lower temperatures where ripplon scattering plays an important role.
  2. On a rotating cryostat, the surface of rotating superfluid is investigated. Ions accumulated under free surface are employed instead of electrons. Manipulation know-how of ions is developed. Preliminary study of surface wave excitation on rotating superfluid was tried. Resonance frequency showed dependence on rotationg speed. The effect may be understood in terms of an inertial wave.
  3. Manipulation of superfluid 3He film is studied by means of inter-digitated capacitors. Experimental cell was assembled to study superfluid 3He film flow under magnetic field.
  4. Fabrication of nanogapped electrodes and trench structure is developed to study electrons on He film and quasi-onedimensional he channels. Electrons on channels from 5 to 20 microns showed size effect in the solidification transition to the Wigner solid. Electrode assembly and detecting device of single electrons have been developed.

Low temperature quantum transport in nano structures

  1. A vertical double quantum dots are fabricated on the basis of GaAs 2D electron gas substrate. Transport properties have been measured under strong magnetic field and Zeeman splitting is observed in a tunnel spectroscopy. The properties are carefully compared with theoretical models to understand the peculiarity of the phenomena.
  2. Effects of light irradiation on to the quantum dots were studied. Photo-creation of electron-hole pair resulted in accumulation of hole inside dots. The accumulated hole act as an effective gate voltage and transport pattern was lifted by light irradiation. By reducing the light intensity, a jump in the transport properties was observed and interpreted by single photon events.
  3. Nanogap electrode is used to trap fine semiconductor particles. Transport property characteristic to Coulomb blockage was observed.
  4. New organic TFTs are developed by the use of nano-fabrication technique.
  5. Structure ordering of proteins is aimed by use of nano-scale template.