Low-bias Transport Features in a Quantum Point Contact with a Variable Aspect Ratio

Quantum Point Contact (QPC) devices frequently display a zero- bias conductance anomaly (ZBA), the origin of which is not fully understood. To investigate a possible connection between the ZBA and the device geometry, we use a four-gate QPC device patterned on a GaAs/AlGaAs semiconductor heterostructure, aiming to achieve independent control over the transverse and the longitudinal potential profiles. In several regimes, we find a narrow ZBA that shows a pronounced temperature dependence for T$<$100 mK. Coulomb peaks arise under certain device settings, suggesting a weakly bound state located in the QPC. For other settings, we observe a plateau below the first conductance step. The plateau's conductance varies as the aspect ratio of the confining potential is changed. We describe a series of magnetic field measurements that show splitting of the ZBA and compare the findings to our measurements in a different, very short device which displayed no ZBA.