Evidence for localization and 0.7 anomaly in hole quantum point contacts

Abstract

Quantum point contacts (QPCs) implemented in p-type GaAs/AlGaAs heterostructures are investigated by low-temperature electrical conductance spectroscopy. Besides one-dimensional conductance quantization, a pronounced extra plateau is found at about 0.7(2<I>e</I><SUP>2</SUP>/<I>h</I>) which possesses the characteristic properties of the so-called "0.7 anomaly" known from experiments with n-type samples. The evolution of the 0.7 plateau in high perpendicular magnetic field reveals the existence of a quasi-localized state and is consistent with the explanation of the 0.7 anomaly based on self-consistent charge localization. These observations are robust when lateral electrical fields are applied which shift the relative position of the electron wave function in the QPC, testifying to the intrinsic nature of the underlying physics.