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
Surface phenomena on quantum systems
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.
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.
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.
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
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.
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.
Nanogap electrode is used to trap fine semiconductor particles.
Transport property characteristic to Coulomb blockage was observed.
New organic TFTs are developed by the use of nano-fabrication
Structure ordering of proteins is aimed by use of nano-scale template.