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Research summary 2008

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. 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.
  2. 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 due 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.
  3. 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. Fabrication of nanogapped electrodes and trench structure is developed to study electrons onHe film and quasi-one dimensional he channels. Nonlinear conductivity of the Wigner solid issystematically studied and analyzed by the Bragg-Cherenkov mechanism. Electrons on channels from 5 to 20 microns showed size effect in the solidification transition to the Wigner solid. Electrode assembly to manipulate single electrons is developed to realize one-dimensional electron array.

Low temperature quantum transport in nano structures

  1. A vertical double quantum dots with different g-factor are fabricated on the basis of GaAs 2D electron gas substrate. Transport properties have been measured under strong magnetic field and the difference in Zeeman splitting results in spin-bottle-neck effects. By tuning the source-drain potential selective trapping of spin up or down is possible. This effect will be used in the initialization process of spin qubits.
  2. Hyperfine interaction between electron and nuclear spins and highly polarized nuclear spins are studied under the Pauli spin blockade regime. By employing g-factor manipulation it is first realized the arbitrary polarization of nuclear spin either up or down. This will be used as a quantum memory.
  3. New nano-structure fabrication technique is developed. Large size graphene sheet is fabricated on SiO2 surface. Further graphene fabrication is under development.
  4. Dynamical nuclear spin polarization by the breakdown of quantum Hall effect is studied.Resistivity detected Nuclear magnetic resonance (NMR), including pulse NMR is observed.