Cryogenic scanning force microscopy of quantum Hall samples: Adiabatic transport originating in anisotropic depletion at contact interfaces

TL;DR

This paper uses cryogenic scanning force microscopy to investigate local potential distributions in quantum Hall samples, revealing anisotropic depletion effects at contact interfaces that influence adiabatic transport.

Contribution

It provides the first microscopic visualization of anisotropic depletion and incompressible strips at contact interfaces in quantum Hall systems.

Findings

Incompressible strips are present at contact interfaces.

Transport features depend on contact orientation.

Local potential measurements reveal microscopic contact effects.

Abstract

Anisotropic magneto resistances and intrinsic adiabatic transport features are generated on quantum Hall samples based on an (Al,Ga)As/GaAs heterostructure with alloyed Au/Ge/Ni contacts. We succeed to probe the microscopic origin of these transport features with a cryogenic scanning force microscope (SFM) by measuring the local potential distribution within the two-dimensional electron system (2DES). These local measurements reveal the presence of an incompressible strip in front of contacts with insulating properties depending on the orientation of the contact/2DES interface line relatively to the crystal axes of the heterostructure. Such an observation gives another microscopic meaning to the term 'non-ideal contact' used in context with the Landauer-B\"uttiker formalism applied to the quantum Hall effect.