450
15 External Fields
15.2.8.3 Weiss Oscillations
In Fig. 15.22, measurements are shown for a Hall bar in which an array of antidots (in which no
conduction is possible) has been introduced by dry etc.hing. The antidot size is 50 nm (plus depletion
layer) and the period is 300 nm. These obstructions for the cyclotron motion lead to a modification of
the magnetotransport properties.
Before etc.hing of the antidot array the 2DEG has a mean free path length of 5–10 µm at 4 K for
the mobility of ≈ 10
6 cm
2 /Vs. At low magnetic fields there is a strong deviation of the Hall resistivity
from the straight line to which the QHE levels converge. Similarly, ρ xx shows a strong effect as well.
These effects are related to commensurability effects between the antidot lattice and the cyclotron
resonance path. When the cyclotron orbit is equal to the lattice period, electrons can fulfill a circular
motion around one antidot (pinned orbit, Fig. 15.22b) that leads to a reduction of conductivity. At high
fields, drifting orbits for which the cyclotron orbit is much smaller than the lattice period occur. At
small fields, scattering orbits also contribute for which the cyclotron radius is large and the electron
has antidots from time to time. Resonances in the Hall resistivity have been found due to pinned orbits
enclosing 1, 2, 4, 9 or 21 antidots.
15 External Fields
15.2.8.3 Weiss Oscillations
In Fig. 15.22, measurements are shown for a Hall bar in which an array of antidots (in which no
conduction is possible) has been introduced by dry etc.hing. The antidot size is 50 nm (plus depletion
layer) and the period is 300 nm. These obstructions for the cyclotron motion lead to a modification of
the magnetotransport properties.
Before etc.hing of the antidot array the 2DEG has a mean free path length of 5–10 µm at 4 K for
the mobility of ≈ 10
6 cm
2 /Vs. At low magnetic fields there is a strong deviation of the Hall resistivity
from the straight line to which the QHE levels converge. Similarly, ρ xx shows a strong effect as well.
These effects are related to commensurability effects between the antidot lattice and the cyclotron
resonance path. When the cyclotron orbit is equal to the lattice period, electrons can fulfill a circular
motion around one antidot (pinned orbit, Fig. 15.22b) that leads to a reduction of conductivity. At high
fields, drifting orbits for which the cyclotron orbit is much smaller than the lattice period occur. At
small fields, scattering orbits also contribute for which the cyclotron radius is large and the electron
has antidots from time to time. Resonances in the Hall resistivity have been found due to pinned orbits
enclosing 1, 2, 4, 9 or 21 antidots.