Resolving the phase of a Dirac topological state via interferometric photoemission

TL;DR

This paper introduces a novel interferometric photoemission technique that reconstructs the phase of electronic states in quantum materials, demonstrated on a topological insulator, revealing phase jumps and helicity of Dirac electrons.

Contribution

It develops a quantum-path electron interferometer using time- and angle-resolved photoemission spectroscopy to measure the phase of electronic states with high resolution.

Findings

Resolved the phase along the Dirac electronic band.

Observed a resonance-associated phase jump.

Demonstrated phase inversion revealing helicity of Dirac cone.

Abstract

The electronic wavefunction is at the heart of physical phenomena, defining the frontiers of quantum materials research. While the amplitude of the electron wavefunction in crystals can be measured with state-of-the-art probes in unprecedented resolution, its phase has remained largely inaccessible, obscuring rich electronic information. Here we develop a quantum-path electron interferometer based on time- and angle-resolved photoemission spectroscopy, that enables the reconstruction of the phase of electronic states in quantum materials - with energy and momentum resolution. We demonstrate the scheme by resolving the phase along the Dirac electronic band of a prototypical topological insulator and observe a resonance-associated phase jump as well as a momentum and phase synchronized inversion revealing the helicity of the Dirac cone. We show the interferometer can be optically controlled by the polarization of the absorbed light, allowing a differential measurement of the phase - a crucial component for extracting phase information from an interferogram. This photo-electron-interferometer is a purely experimental scheme and does not rely on any specific theoretical model. It can be extended to a variety of materials, opening up the phase dimension in quantum materials research.