Electron backscattering in a cavity: ballistic and coherent effects

TL;DR

This study investigates how conductance in a quantum point contact evolves as a cavity forms, revealing coexistence of quantum interference effects and classical trajectories, with new insights into electron backscattering in chaotic systems.

Contribution

It demonstrates the formation of branches and interference fringes during cavity development, highlighting effects of the stadium potential on conductance and backscattering patterns.

Findings

Branches exist only within cavity top gates.

Regular fringes from tip-induced constrictions lead to quantized conductance.

Arc-like regions indicate classical electron trajectories.

Abstract

Numerous experimental and theoretical studies have focused on low-dimensional systems locally perturbed by the biased tip of a scanning force microscope. In all cases either open or closed weakly gate-tunable nanostructures have been investigated, such as quantum point contacts, open or closed quantum dots, etc. We study the behaviour of the conductance of a quantum point contact with a gradually forming adjacent cavity in series under the influence of a scanning gate. Here, an initially open quantum point contact system gradually turns into a closed cavity system. We observe branches and interference fringes known from quantum point contacts coexisting with irregular conductance fluctuations. Unlike the branches, the fluctuations cover the entire area of the cavity. In contrast to previous studies, we observe and investigate branches under the influence of the confining stadium potential, which is gradually built up. We find that the branches exist only in the area surrounded by cavity top gates. As the stadium shrinks, regular fringes originate from tip-induced constrictions leading to quantized conduction. In addition, we observe arc-like areas reminiscent of classical electron trajectories in a chaotic cavity. We also argue that electrons emanating from the quantum point contact spread out like a fan leaving branch-like regions of enhanced backscattering.