Low Temperature Scanning Force Microscopy for Probing the Edge of Quantum Hall Systems

Using our recently implemented ultra-low temperature, high magnetic field scanning force microscope, we have further developed methods to probe charge transport in semiconductor materials, specifically edge states of a 2-dimensional electron gas (2DEG) in the quantum hall regime. Among other techniques, we apply an AC excitation signal to a buried two-dimensional electron gas and monitor the electrostatic potential distribution via the oscillation dynamics of a piezoelectric quartz tuning fork with an etched metallic probe attached to one tine. The quartz tuning fork allows for ultrasensitive detection of electric forces as a consequence of its small oscillation amplitude. Additionally, the 2DEG sample is prepared with a cleaved edge overgrowth structure offering an extra electrode separated from the 2DEG by a atomically defined tunneling barrier, resulting in an addressable edge.