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Research summary 2010

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. Supersolid properties in solid He is studied under rotation. Millimeter wave absorption induced resistance of surface state electrons on liquid He is studied under magnetic fields, where diminishing resistance is observed. Coherent nuclear spin manipulation is achieved in vertical double quantum dots by means of electric potential and RF pulse. Spatial distribution of dynamical nuclear spin polarization is studied in the quantum Hall effect breakdown regime. Quantum transport measurement is done under ultralow temperature environment.

Surface phenomena on quantum systems

  1. Transport properties of 2D electrons on liquid He under millimeter wave irradiation (D. Konstantinov, K. Kono)

    The excitation of surface state electrons by irradiating 100GHz range millimeter wave induces a prominent transport effect. Under strong magnetic fields the resistance exhibited novel magneto-oscillations and the resistance eventually shows zero resistance states.

  2. 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, we have measured the conductivity of ion pools below the surface.

  3. Transport properties of point-contact in electrons on liquid He (D. Ress, K. Kuroda, M. Hoefer, P. Leiderer, K. Kono)

    By employing nanogapped electrodes and capillary-condensed He channels, a point-contact device is fabricated. The point-contact device shows step-like I-V characteristics, which are ascribed to the granularity of electrons and charging energy.

  4. Study of supersolid He under rotation (H. Choi, E. Kim, D. Takahashi, K. Kono)

    Torsional oscillator response of solid helium is studied under rotation together with rigidity. The result is naturally interpreted by a supersolid model.

  5. Spectroscopy of Ba ions under a free surface of liquid He (M. Watanabe, M. Schmotz, R. Batulin, K. Kono)

    In order to study Majorana nature of surface bound states under a free surface of superfluid 3He, spectroscopy of Ba ion is developed. This year a laser aberration is tried to produce Ba ions in liquid He.

Low temperature quantum transport in nano structures

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

    Coherent and bi-directional nuclear spin manipulation is demonstrated in vertical double quantum dots. Application of electric potential and rf-NMR pulses achieve an arbitrary polarization of coherent nuclear. This will be used in a technology of quantum memory.

  2. Manipulation of three spins in double quantum dot(S. Amaha, K. Ono, K. Kono)

    Novel spin blockade for three electron spins are found in double quantum dots. This will be used for initializing multi spin qubits.

  3. Breakdown of quantum Hall effect and nuclear spin polarization (M. Kawamura, and K. Kono)

    We have studied dynamical nuclear spin polarization induced by the breakdown of quantum Hall effect. We conducted experiments using multi-terminal Hall-bar devices and found that the amplitudes of nuclear magnetic resonance signals from the polarized nuclear spins depend on the distance from the electron-injecting electrode. This result directly shows that the dynamic nuclear spin polarization has a spatial gradient in the device. The spatial gradient is explained by the avalanche-type breakdown mechanism of the quantum Hall effect

  4. Ultra-low temperature measurement of semiconductor quantum dot transport properties (A. Badrutdinov, SM. Huang, H. Akimoto, K. Ono, H. Ikegami, H. Ishimoto, K. Kono)

    Spin blockade and nuclear spin effects are studied down to sub-mili Kelvin temperature. An enhancement of nuclear spin decay time is observed.