Search

We investigate background charge fluctuation in a GaAs quantum dot device by measuring 1/f noise in the single-electron tunneling current through the dot. The current noise is understood as fluctuations of the confinement potential and tunneling barriers. The estimated potential fluctuation increases almost linearly with temperature, which is consistent with a simple model of the 1/f noise. We find that the fluctuation increases very slightly when electrons are injected into excited states of the quantum dot. [ABSTRACT FROM AUTHOR]

Single-electron tunneling through a quantum dot is detected by means of a radio-frequency single-electron transistor. Poisson statistics of single-electron tunneling events are observed from frequency domain measurements, and individual tunneling events are detected in the time-domain measurements. Counting tunneling events gives an accurate current measurement in the saturated current regime, where electrons tunnel into the dot only from one electrode and tunnel out of the dot only to the other electrode. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Edge magnetoplasmon (EMP) transport in gated and ungated quantum Hall systems is investigated by time-of-flight measurements. We measured the velocity, the amplitude, and the broadening of the EMP pulse injected by applying a voltage pulse to an Ohmic contact. We show that the transverse width of EMPs in the ungated sample is determined by the potential profile in the edge region, independent of the filling factor. In the gated sample, on the other hand, EMPs are confined by the innermost incompressible strip and their transverse width depends on the filling factor and the bulk electron density. We also find that scattering of EMPs by the bulk electrons is modified by the presence of the gate. [ABSTRACT FROM AUTHOR]

The tunneling rates for spin-up and -down electrons are investigated for a GaAs quantum dot in an in-plane magnetic field by using a real-time single-electron counting scheme with a nearby charge detector. An extremely small spin-polarized current on the order of attoamperes is analyzed with the spin and energy dependences of the tunneling rates. Fully spin-polarized current is obtained when only a spin-up Zeeman sublevel is located in the transport window. When both Zeeman sublevels are allowed to contribute to the transport, we find that the tunneling rate for spin-up electrons is considerably higher than that for spin-down electrons. This partially spin-polarized current can be explained by the exchange-enhanced spin splitting in low-density regions near the tunneling barriers. [ABSTRACT FROM AUTHOR]

We investigate how the orbital magnetic moments of electron and hole states in a carbon nanotube quantum dot depend on the number of carriers on the dot. Low temperature transport measurements are carried out in a setup where the device can be rotated in an applied magnetic field, thus enabling accurate alignment with the nanotube axis. The field dependence of the level structure is measured by excited state spectroscopy and excellent correspondence with a single-particle calculation is found. In agreement with band structure calculations we find a decrease of the orbital magnetic moment with increasing electron or hole occupation of the dot, with a scale given by the band gap of the nanotube. [ABSTRACT FROM AUTHOR]

Electron-cooling experiments have been carried out at the HIMAC-synchrotron in order to provide high-quality beams for medical and related research. For investigating the behavior of the free radicals, especially, the beam bunch was compressed by electron cooling with a triangle-wave RF-field. The dependences of the bunch length on the electron energy and the RF voltage were investigated under various intensities of Ar18+ beam. As a result, the bunch length was limited by around 20 ns due to the space-charge effect under an intensity of 1.33×106 ions/bunch and an RF amplitude of 340 V. [Copyright &y& Elsevier]