Direct measurement of key exciton properties: energy, dynamics and spatial distribution of the wave function

TL;DR

This study uses multidimensional photoemission spectroscopy to directly measure and visualize key properties of excitons, including energy, dynamics, and spatial distribution, in a layered semiconductor, providing comprehensive insight into excitonic behavior.

Contribution

It introduces a novel experimental approach to directly access and reconstruct the excitonic wave function and related properties in semiconductors, aligning well with theoretical predictions.

Findings

Determined the energy-momentum signature of bright excitons.

Reconstructed the real-space excitonic distribution function.

Measured exciton binding energy and lattice coupling.

Abstract

Excitons, Coulomb-bound electron-hole pairs, are the fundamental excitations governing the optoelectronic properties of semiconductors. While optical signatures of excitons have been studied extensively, experimental access to the excitonic wave function itself has been elusive. Using multidimensional photoemission spectroscopy, we present a momentum-, energy- and time-resolved perspective on excitons in the layered semiconductor WSe$_2$. By tuning the excitation wavelength, we determine the energy-momentum signature of bright exciton formation and its difference from conventional single-particle excited states. The multidimensional data allows to retrieve fundamental exciton properties like the binding energy and the exciton-lattice coupling and to reconstruct the real-space excitonic distribution function via Fourier transform. All quantities are in excellent agreement with microscopic calculations. Our approach provides a full characterization of the exciton properties and is applicable to bright and dark excitons in semiconducting materials, heterostructures and devices.