954 research outputs found
Imaging the lateral shift of a quantum-point contact using scanning-gate microscopy
We perform scanning-gate microscopy on a quantum-point contact. It is defined
in a high-mobility two-dimensional electron gas of an AlGaAs/GaAs
heterostructure, giving rise to a weak disorder potential. The lever arm of the
scanning tip is significantly smaller than that of the split gates defining the
conducting channel of the quantum-point contact. We are able to observe that
the conducting channel is shifted in real space when asymmetric gate voltages
are applied. The observed shifts are consistent with transport data and
numerical estimations.Comment: 5 pages, 3 figure
Gating of high-mobility two-dimensional electron gases in GaAs/AlGaAs heterostructures
We investigate high-mobility two-dimensional electron gases in AlGaAs
heterostructures by employing Schottky-gate-dependent measurements of the
samples' electron density and mobility. Surprisingly, we find that two
different sample configurations can be set in situ with mobilities diering by a
factor of more than two in a wide range of densities. This observation is
discussed in view of charge redistributions between the doping layers and is
relevant for the design of future gateable high-mobility electron gases
Scanning-gate-induced effects and spatial mapping of a cavity
Tailored electrostatic potentials are the foundation of scanning gate
microscopy. We present several aspects of the tip-induced potential on the
two-dimensional electron gas. First, we give methods on how to estimate the
size of the tip-induced potential. Then, a ballistic cavity is formed and
studied as a function of the bias-voltage of the metallic top gates and probed
with the tip-induced potential. It is shown how the potential of the cavity
changes by tuning the system to a regime where conductance quantization in the
constrictions formed by the tip and the top gates occurs. This conductance
quantization leads to a unprecedented rich fringe pattern over the entire
structure. Finally, the effect of electrostatic screening of the metallic top
gates is discussed.Comment: 10 pages, 6 figure
Locally induced quantum interference in scanning gate experiments
We present conductance measurements of a ballistic circular stadium
influenced by a scanning gate. When the tip depletes the electron gas below, we
observe very pronounced and regular fringes covering the entire stadium. The
fringes correspond to transmitted modes in constrictions formed between the
tip-induced potential and the boundaries of the stadium. Moving the tip and
counting the fringes gives us exquisite control over the transmission of these
constrictions. We use this control to form a quantum ring with a specific
number of modes in each arm showing the Aharonov-Bohm effect in low-field
magnetoconductance measurements.Comment: 10 pages, 4 figure
Pattern formation and localization in the forced-damped FPU lattice
We study spatial pattern formation and energy localization in the dynamics of
an anharmonic chain with quadratic and quartic intersite potential subject to
an optical, sinusoidally oscillating field and a weak damping. The
zone-boundary mode is stable and locked to the driving field below a critical
forcing that we determine analytically using an approximate model which
describes mode interactions. Above such a forcing, a standing modulated wave
forms for driving frequencies below the band-edge, while a ``multibreather''
state develops at higher frequencies. Of the former, we give an explicit
approximate analytical expression which compares well with numerical data. At
higher forcing space-time chaotic patterns are observed.Comment: submitted to Phys.Rev.
Irreversibility on the Level of Single-Electron Tunneling
We present a low-temperature experimental test of the fluctuation theorem for
electron transport through a double quantum dot. The rare entropy-consuming
system trajectories are detected in the form of single charges flowing against
the source-drain bias by using time-resolved charge detection with a quantum
point contact. We find that these trajectories appear with a frequency that
agrees with the theoretical predictions even under strong nonequilibrium
conditions, when the finite bandwidth of the charge detection is taken into
account
- …