Geometry Dependence of Quantum Point Contact Conductance*

We present evidence that quantum point contacts (QPCs) fabricated on a high mobility (~10⁶ cm²/Vs) GaAs/AlGaAs heterstructure crystal with doping close to the 2D interface exhibit quantum transport conductance which is strongly dependent on the QPC geometry. In particularly, asymmetrically shaped, T-junction QPCs nearly always exhibit strong conductance resonances as well as anomalies in the conductance plateaus, whereas symmetrically shaped QPCs, designed with smooth entrance and exit regions joining to wide 2D regions, are largely devoid of such resonances. The dramatic difference in the conductance traces between the two types of geometries suggest that disorder does NOT play a dominant role in the transport characteristics. Furthermore, this implies that unusal features, including resonances, suppression of quantum plateaus[1,2], and novel differential conductance oscillations [3] previously reported in asymmetric QPCs could arise instead from intrinsic mechanisms, e.g. geometry and/or interaction effects.
[1] P.M. Wu, P, Li, H. Zhang, and A.M. Chang, Phys. Rev. B 85, 085305 (2012).
[2] H. Zhang, P.M. Wu, and A.M. Chang, Phys. Rev. B 88, 075311 (2013).
[3] H. Zhang, P.M. Wu, and A.M. Chang, Phys. Rev. B 91, 195150 (2015).