Microwave investigations of semiconductor quantum dots

In semiconductor quantum dots many basic physical phenomena can be studied. They also have the potential of future applications, e.g. in microelectronics, opto-electronics, and quantum computing. In the proposed project transport effects in the presence of high-frequency fields shall be studied. The quantum dots will be fabricated from AlGaAs/GaAs heterostructures and defined by split-gate structures (cooperations with Technical University of Vienna, Austria and RIKEN, Japan). Depending on the strength of the coupling to reservoirs (source and drain) the dots are termed "closed" or "open". The effect of the high-frequency fields on the dc or low-frequency conductance will be measured. Beside characterization measurements at zero-field the experiments will be performed in magnetic fields (up to 17T). The frequencies used will be in the microwave and millimeter wave range (approx. 20- 170 GHz). This is a frequency range appropriate for resonance experiments (electron spin resonance (ESR); transitions between confinement-related dot levels) as well as for non-resonant experiments (high-frequency dephasing). The main tasks of the project concern: (1) Coulomb blockade effects in closed dots: Experiments at Landau level filling larger than 1 shall provide the information on the quality of the dots and also the basis for the extension to fractional filling below 1 as well as for the ESR experiments. Whether Coulomb blockade effects with composite fermions occur is a particularly interesting question of quantum dot physics. (2) ESR in closed and open dots: The mechanisms causing an ESR signal in the conductance will be studied first. In closed dots it is expected that an ESR-induced internal charge redistribution causes a modification of the Coulomb oscillations. In open dots it shall be clarified if the same mechanism or another one, e.g. a change of the backscattering, can be used for detecting the ESR. A main aim is to study many-body effects in the ESR over a wide frequency range. (3) Conductance fluctuations in open dots: The conductance fluctuations are related to the varying degree of backscattering of the electrons in the dot. This leads to fluctuations of the conductance as a function of magnetic field or gate voltage. A goal of this project is to find out whether zero-dimensional dot levels play a significant role and whether a direct dephasing effect of high-frequency fields exists (not only an electron heating effect).

In semiconductor quantum dots many basic physical phenomena can be studied. They also have the potential of future applications, e.g. in microelectronics, opto-electronics, and quantum computing. In the proposed project transport effects in the presence of high-frequency fields shall be studied. The quantum dots will be fabricated from AlGaAs/GaAs heterostructures and defined by split-gate structures (cooperations with Technical University of Vienna, Austria and RIKEN, Japan). Depending on the strength of the coupling to reservoirs (source and drain) the dots are termed "closed" or "open". The effect of the high-frequency fields on the dc or low-frequency conductance will be measured. Beside characterization measurements at zero-field the experiments will be performed in magnetic fields (up to 17T). The frequencies used will be in the microwave and millimeter wave range (approx. 20- 170 GHz). This is a frequency range appropriate for resonance experiments (electron spin resonance (ESR); transitions between confinement-related dot levels) as well as for non-resonant experiments (high-frequency dephasing). The main tasks of the project concern: 1. Coulomb blockade effects in closed dots: Experiments at Landau level filling larger than 1 shall provide the information on the quality of the dots and also the basis for the extension to fractional filling below 1 as well as for the ESR experiments. Whether Coulomb blockade effects with composite fermions occur is a particularly interesting question of quantum dot physics. 2. ESR in closed and open dots: The mechanisms causing an ESR signal in the conductance will be studied first. In closed dots it is expected that an ESR-induced internal charge redistribution causes a modification of the Coulomb oscillations. In open dots it shall be clarified if the same mechanism or another one, e.g. a change of the backscattering, can be used for detecting the ESR. A main aim is to study many-body effects in the ESR over a wide frequency range. 3. Conductance fluctuations in open dots: The conductance fluctuations are related to the varying degree of backscattering of the electrons in the dot. This leads to fluctuations of the conductance as a function of magnetic field or gate voltage. A goal of this project is to find out whether zero-dimensional dot levels play a significant role and whether a direct dephasing effect of high-frequency fields exists (not only an electron heating effect).