Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

Abstract

Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between aFermi liquid and Wigner crystal, are predicted to exhibit complex local charge order.Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this Letter, we present our progress in developing a technique called "virtual scanning tunneling microscopy" that allows local tunneling into a high mobility 2DES. Using a specially-designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-200 nm resolution.

Versatile Millikelvin Hybrid Cooling Platform for Superconductivity Research

“…Several cryogenic scanning probe microscopes have been already realized in closed cycle cryostats. They include scanning gate microscopy [8,9], scanning tunneling microscopy [10], and scanning SQUID microscopy [11][12][13][14][15][16][17][18][19]. In most of these systems, a rigid scanner or decoupling of vibrations through flexible thermal links or a combination of the two mitigation methods were implemented.…”

Imaging Anyons with Scanning Tunneling Microscopy

“…Until recently, STM in the bulk of a FQH state was largely impractical, since the pristine 2DEGs required were only possible to realize in quantum wells sandwiched deep between semiconductors (though workarounds have been proposed [8,9]). The observation of QH effects in graphene [10] and the surface states of bismuth, [11] where the 2DEG is atomically close to the vacuum, removes this obstacle.…”