

Research summary 2009
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. Nonlinear transport
of ion pool trapped under the surface of superfluid 4He was
studied.Millimeter wave absorption induced resistance of surface sate
elecrons on liquid He is studied under strong excitation limit, where
distortion of resonance curve and hysteretic behavior areobserved. A
vertical double quantum dots with different gfactor based on GaAs
semiconductor was fabricated and transport properties under high
magnetic fields has been studied. Interaction between electron spin
and nuclear spin and nuclear spin polarization are studied in the
doublequantum dot and quantum Hall effect breakdown regime.
Fabrication of new nanostructure is carried out.
Surface phenomena on quantum systems

Transport properties of 2D electrons on liquid He under millimeter
wave irradiation (D. Konstantinov, M. Dykman, Y. Monarkha, K. Kono)
The excitation of surface state electrons by irradiating 100GHz range
millimeter wave induces a prominent resistivity increase. Under strong
excitation conditions the resonance curve showed distortion and
hysteresis. The effect is attributed to the strong electronelectron
interaction. Application of a magnetic field perpendicular to the
surface results in a Landau quantization of 2Delectron states. By
employing the resistance measurement under irradiation of millimeter
wave exhibited novel magnetoresistivity oscillations.

Nonlinear transport properties of ion pools under a free surface of
rotating superfluid He (D. Takahashi, H. Ikegami, K. Kono)
Nonlinear transport of ion pools under the surface of superfluid is
investigated to find abrupt transition to low mobility regime by
increasing the ion velocity. The transition is attributed to the
creation of quantum vortices and its tangle. The temperature
dependence of critical velocity decreases by lowering temperature,
striking contrast to the thermal excitation process. Macroscopic
tunneling mechanism is suggested. The temperature dependence seems to
imply the reduction of tunneling rate because of quantum
friction. Plasmon resonance is also measured under rotation. The
resonance frequency and line width increased linearly with rotation
speed.

Twodimensional superfluid ^{3}He films (M. Saitoh,
H. Ikegami, K. Kono)
Manipulation of superfluid ^{3}He film is studied by means of
interdigitated capacitors. Thickness dependence of the superfluidity
onset temperature is measured in detail and quantitative disagreement
with naive theory is found. The phenomena is studied also under
magnetic field and parallel effect is found.

Transport properties of ion pools under a free surface of superfluid
^{3}He (T. Matsumoto, H. Ikegami, K. Kono)
Aiming the detection of surface bound states in the vicinity of free
surface of superfluid ^{3}He, preliminary experiment is
carried out to measure the conductivity of ion pools below the
surface.

Transport properties of electrons on adsorbed He films and capillary
condensed channels (K. Kuroda, M. Hoefer, H. Akimoto, A. Suzuki,
M. Watanabe, P. Leiderer, K. Kono)
Fabrication of nanogapped electrodes and trench structure is developed
to study electrons on He film and quasione dimensional He channels. A
size effect in the solidification transition to the Wigner solid is
analysed. Electrode assembly to manipulate single electrons is
developed to realizeonedimensional electron array. A nanofabricated
splitgate device was used to measure the conductance of the electron
system in a small constriction, as in a pointcontact device. To
approach Fermi degenerate electrons systems, electrons on saturated He
films of about 30 nm thickness are studied. To eliminate
uncontrollability due to stray charges, energy selective electron
source is being developed.
Low temperature quantum transport in nano structures

Resonant tunneling effect in semiconductor double quantum dot device
(YC. Sun, SM. Huang, H. Akimoto, K. Ono, JJ. Lin, K. Kono)
Vertical double quantum dots made of GaAs and InGaAs with different
gfactors are fabricated. Resonant tunneling properties have been
measured under strong magnetic field. Sampledependence of
spinbottleneck effect, which results from the difference in Zeeman
splitting, has been studied.

Nuclear spin effect in semiconductor quantum dots (R. Takahashi,
K. Ono, K. Kono)
Nuclear spin manipulation by means of Pauli spinblockade effect is
studied. An arbitrarypolarization of nuclear spin either up or down
is achieved only by application of electric potential. This will be
used in a technology of quantum memory.

Manipulation of opticalphonons in semiconductor quantum dots (K. Ono,
K. Kono)
Single electron transport associated with optical phonon emission is
observed. This phenomenon will be used to control the optical phonon
number state.

Break down of quantum Hall effect and nuclear spin polarization
(M. Kawamura, D. Gottwald, K. Kono)
Dynamical nuclear spin polarization by the breakdown of quantum Hall
effect and resistivity detected nuclear magnetic resonance (NMR) are
studied. By employing this effect one can possible to detect NMR
signal with spatial resolution. From the measurement of Knight shift,
energy relaxation time, and phase relaxation time, it is found that
the electrons spin polarizationunder quantum Hall effect has spatially
inhomogeneous.

Ultralow temperature measurement of semiconductor quantum dot
transport properties (A. Badrutdinov, SM. Huang, H. Akimoto, K. Ono,
H. Ikegami, H. Ishimoto, K. Kono)
To measure the transport properties of semiconductor quantum dots in
an ultralow temperature region, nuclear demagnetization cryostat is
being constructed. An effect originated from nuclear and electron spin
interaction in this temperature range is estimated.

