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Research summary 2005

We study prominent quantum phenomena in condensed matter in a wide temperature range including micro Kelvin region. Ultra-low tempearture facility is established and we started the experiment on 2D electrons on superfluid 3He. Rotating cryostat starts working. Millimeter wave absorption because of transitions between electronic surface states on liquid He is observed. In order to fabricate vertical quantum dots based on GaAs semiconductor, we introduced ECR dry-etching equipment. The quantum dots may be used for quantum information processing.

Surface phenomena on quantum systems

  1. The resistivity measurement of the Wigner solid on supeerfluid 3He under a magnetic field is carried out. The observation on A-pahse shows a clear evidence for gap nodes.
  2. On a rotating cryostat, the mobility of 2D electrons on rotating superfluid is measured. Magnetoresistance shows a prominent rotation depndence.
  3. To control and detect single electrons on liquid He surface and to develop quantum computing, the excitation of surface state electrons by irradiating 130GHz millimeter wave is tried. Absorption of millimeter wave is observed and temperature dependence of linewidth and shape is studied.
  4. Transport of 2D electrons on a thin helium film is studied. Capillary condensed quasi-one-dimensional channel is used to meaure the conductivity of electrons supported by the channel.

Low temperature quantum transport in nano structures

  1. An ECR dry-etching equipment is introduced and the performance was tuned in order to fabricate a GaAs based quantum dots.
  2. Mesoscopic Hall probe made from GaAs heterostructure is improved to detect the spatial distribution of flux quanta in mesoscopic superconductor structures.
  3. Quantum transport of atomic contact controlled by a mechanical-break-junction technique is carried out at dilution temperatures. Superconducting properties of an atomic contact is studied in Al. A break junction of organic conductor is made and conductance quatization at a half-integer is observed.
  4. A prominent single electron charging effect, or Coulomb diamond was observed at 4K in single gold particle of 10 nanometer in diameter. A nolinear behaviour is attributed to the transport peculiality of sandwitched molecules.
  5. New organic TFTs are developed by the use of nano-fabrication technique.