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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 g-factor 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 nano-structure is carried out.

Surface phenomena on quantum systems

  1. 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 electron-electron 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.

  2. 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.

  3. Two-dimensional superfluid 3He films (M. Saitoh, H. Ikegami, K. Kono)

    Manipulation of superfluid 3He film is studied by means of inter-digitated 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.

  4. Transport properties of ion pools under a free surface of superfluid 3He (T. Matsumoto, H. Ikegami, K. Kono)

    Aiming the detection of surface bound states in the vicinity of free surface of superfluid 3He, preliminary experiment is carried out to measure the conductivity of ion pools below the surface.

  5. 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 quasi-one 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 realizeone-dimensional electron array. A nano-fabricated split-gate device was used to measure the conductance of the electron system in a small constriction, as in a point-contact 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

  1. 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 g-factors are fabricated. Resonant tunneling properties have been measured under strong magnetic field. Sampledependence of spin-bottle-neck effect, which results from the difference in Zeeman splitting, has been studied.

  2. Nuclear spin effect in semiconductor quantum dots (R. Takahashi, K. Ono, K. Kono)

    Nuclear spin manipulation by means of Pauli spin-blockade 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.

  3. Manipulation of optical-phonons 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.

  4. 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.

  5. 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.