Electron Transport of Antidot Systems in the Quantum Hall Regime
Masanori Kato
Doctoral Thesis, University of Tokyo (2009)
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Note: Doctoral Thesis, University of Tokyo
In this thesis, we investigated the electron transport of antidot systems, \textit {i.e.}, potential hills for two-dimensional (2D) electrons, in the quantum Hall (QH) regime.
We measured two-types of samples based on GaAs/AlGaAs heterostructures. One is the antidot lattice, that is a periodic potential modulation to two-dimensional electron system, and the other is the single antidot, that is one antidot between metal side gates.
We focused on Aharonov-Bohm (AB)-type oscillations, \textit {i.e.}, periodic magnetoresistance oscillations, in the QH regime and explored
the electron properties of the edge states bounded around antidots: screening effects, spin polarization, and so on.
Firstly, we studied various aspects of the AB-type oscillations in antidot lattices in the QH regime. We confirmed that the AB-type oscillation in the
QH regime originates from the fine structure in the density of states created by the quantization of edge states circumnavigating each antidot.
This picture was supported by the fact that the characteristic energy scales obtained from the temperature dependence of the oscillation amplitude and from the gate bias dependence agree with each other.
Features associated with spin-resolved edge channels formed around the antidots were also observed in the vicinity of the Landau level filling factor $\nu = 2$.
Secondly, we measured the evolution of the AB-type oscillations of the lattice sample in the magnetic field-gate voltage ($B$-$V_\mathrm g$) plane in order to evaluate the potential gradient of the antidot.
The potential profile of the edge states is much flatter than the bare potential due to the screening effect.
Then we investigated the temperature dependence of the potential profile.
The experimental results suggest that the gradient become larger with increasing temperature as a result of the reduction of screening.
Finally, we investigated resonant tunneling through a single antidot in the QH regime.
When the two edge states with different spins of the lowest Landau level are localized around the antidot, or the filling factor around the antidot is two, the conductance exhibit the paired $h/2e$
AB(-type) oscillations.
Using a tilted magnetic field technique we observed the evolution of the oscillations and a concomitant change in the conduction spectra at finite source-drain bias with the total magnetic field, and we extracted the effectiveness of the Zeeman energy to the AB(-type) oscillations.