RESEARCH ARTICLE

Real- and momentum-indirect neutral and charged excitons in a multi-valley semiconductor

¹ Beijing National Laboratory for Condensed Matter Physics, Key Laboratory for Nanoscale Physics and Devices, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
² School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
³ Ningbo Institute of Materials Technology & Engineering, Chinese Academy of Sciences, Ningbo 315201, China
⁴ Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
⁵ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
⁶ Department of Electronics and Nanoengineering, Aalto University, Tietotie 3, Espoo FI-02150, Finland
⁷ Quantum Technology Finland (QTF) Centre of Excellence, Department of Applied Physics, Aalto University, Aalto FI-00076, Finland
⁸ Beijing Key Laboratory for Nanomaterials and Nanodevices, Beijing 100190, China
⁹ Songshan Lake Materials Laboratory, Dongguan 523808, China

^* Corresponding authors (emails: sxdu@iphy.ac.cn (Shixuan Du); luojun.du@iphy.ac.cn (Luojun Du); gyzhang@iphy.ac.cn (Guangyu Zhang))

Received: 30 September 2022
Revised: 2 January 2023
Accepted: 16 January 2023

Abstract

Excitons dominate the photonic and optoelectronic properties of a material. Although significant advancements exist in understanding various types of excitons, progress on excitons that are indirect in both real- and momentum-spaces is still limited. Here, we demonstrate the real- and momentum-indirect neutral and charged excitons (including their phonon replicas) in a multi-valley semiconductor of bilayer MoS₂, by performing electric-field/doping-density dependent photoluminescence. Together with first-principles calculations, we uncover that the observed real- and momentum-indirect exciton involves electron/hole from K/Γ valley, solving the longstanding controversy of its momentum origin. Remarkably, the binding energy of real- and momentum-indirect charged exciton is extremely large (i.e., ~59 meV), more than twice that of real- and momentum-direct charged exciton (i.e., ~24 meV). The giant binding energy, along with the electrical tunability and long lifetime, endows real- and momentum-indirect excitons an emerging platform to study many-body physics and to illuminate developments in photonics and optoelectronics.