Mode Spectroscopy and Level Coupling in Ballistic Electron Waveguides

TL;DR

This paper investigates mode coupling in ballistic electron waveguides using magnetotransport experiments, revealing how magnetic fields influence subband interactions and extending the Darwin-Fock model to describe these effects.

Contribution

It introduces a method to analyze mode spectrum and coupling in quantum point contacts with multi-directional modes, extending existing models to include nonparabolic confinement effects.

Findings

Magnetic field couples modes along the current direction.

Anticrossings observed as a function of magnetic field.

Mode coupling due to nonparabolic confinement effects.

Abstract

A tunable quantum point contact with modes occupied in both transverse directions is studied by magnetotransport experiments. We use conductance quantization of the one-dimensional subbands as a tool to determine the mode spectrum. A magnetic field applied along the direction of the current flow couples the modes. This can be described by an extension of the Darwin-Fock model. Anticrossings are observed as a function of the magnetic field, but not for zero field or perpendicular field directions, indicating coupling of the subbands due to nonparabolicity in the electrical confinement.