Linear conductance of quantum point contacts with deliberately broken symmetry

We investigate the linear transport properties of quantum point contacts (QPCs) whose symmetry is deliberately broken in a controlled manner. The devices that we study consist of a conventional split-gate QPC, which is modified by the inclusion of an additional perturbing gate that is used to modulate the electron density on one side of the device. As the voltage applied to this 'finger gate' is varied, we observe several reproducible features below the last integer plateau, as well as strong modifications of the integer-plateau staircase. Self-consistent calculations, performed for the exact device structure utilized in experiment, suggest that these features are related to the ability of the finger gate to strongly disrupt the symmetry of the QPC, reducing the electron density significantly on one side of the device. We discuss these results within the context of recent models for many-body electron transport in QPCs.