skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides

Abstract

Monolayer transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) semiconductors for application in optoelectronics. Their optical properties are dominated by two series of photo-excited exciton states—A (XA) and B (XB) 1,2 —that are derived from direct interband transitions near the band extrema. These exciton states have large binding energies and strong optical absorption 3–6 , and form an ideal system to investigate many-body effects in low dimensions. Because spin–orbit coupling causes a large splitting between bands of opposite spins, XA and XB are usually treated as spin-polarized Ising excitons, each arising from interactions within a specific set of states induced by interband transitions between pairs of either spin-up or spin-down bands (TA or TB). Here, by using monolayer MoS 2 as a prototypical system and solving the first-principles Bethe–Salpeter equations, we demonstrate a strong intravalley exchange interaction between TA and TB, indicating that XA and XB are mixed states instead of pure Ising excitons. Using 2D electronic spectroscopy, we observe that an optical excitation of the lower-energy TA induces a population of the higher-energy TB, manifesting the intravalley exchange interaction. This work elucidates the dynamics of exciton formation in monolayer TMDCs, and sheds light on many-body effects in 2D materials.

Authors:
; ORCiD logo; ORCiD logo; ; ORCiD logo; ORCiD logo;
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1581333
DOE Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 15; Journal Issue: 3; Journal ID: ISSN 1745-2473
Publisher:
Nature Publishing Group (NPG)
Country of Publication:
United States
Language:
English

Citation Formats

Guo, Liang, Wu, Meng, Cao, Ting, Monahan, Daniele M., Lee, Yi-Hsien, Louie, Steven G., and Fleming, Graham R. Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides. United States: N. p., 2018. Web. doi:10.1038/s41567-018-0362-y.
Guo, Liang, Wu, Meng, Cao, Ting, Monahan, Daniele M., Lee, Yi-Hsien, Louie, Steven G., & Fleming, Graham R. Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides. United States. https://doi.org/10.1038/s41567-018-0362-y
Guo, Liang, Wu, Meng, Cao, Ting, Monahan, Daniele M., Lee, Yi-Hsien, Louie, Steven G., and Fleming, Graham R. Mon . "Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides". United States. https://doi.org/10.1038/s41567-018-0362-y.
@article{osti_1581333,
title = {Exchange-driven intravalley mixing of excitons in monolayer transition metal dichalcogenides},
author = {Guo, Liang and Wu, Meng and Cao, Ting and Monahan, Daniele M. and Lee, Yi-Hsien and Louie, Steven G. and Fleming, Graham R.},
abstractNote = {Monolayer transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) semiconductors for application in optoelectronics. Their optical properties are dominated by two series of photo-excited exciton states—A (XA) and B (XB) 1,2 —that are derived from direct interband transitions near the band extrema. These exciton states have large binding energies and strong optical absorption 3–6 , and form an ideal system to investigate many-body effects in low dimensions. Because spin–orbit coupling causes a large splitting between bands of opposite spins, XA and XB are usually treated as spin-polarized Ising excitons, each arising from interactions within a specific set of states induced by interband transitions between pairs of either spin-up or spin-down bands (TA or TB). Here, by using monolayer MoS2 as a prototypical system and solving the first-principles Bethe–Salpeter equations, we demonstrate a strong intravalley exchange interaction between TA and TB, indicating that XA and XB are mixed states instead of pure Ising excitons. Using 2D electronic spectroscopy, we observe that an optical excitation of the lower-energy TA induces a population of the higher-energy TB, manifesting the intravalley exchange interaction. This work elucidates the dynamics of exciton formation in monolayer TMDCs, and sheds light on many-body effects in 2D materials.},
doi = {10.1038/s41567-018-0362-y},
url = {https://www.osti.gov/biblio/1581333}, journal = {Nature Physics},
issn = {1745-2473},
number = 3,
volume = 15,
place = {United States},
year = {2018},
month = {12}
}

Works referenced in this record:

Atomically Thin MoS2 A New Direct-Gap Semiconductor
journal, September 2010


Emerging Photoluminescence in Monolayer MoS2
journal, April 2010


Optical Spectrum of MoS 2 : Many-Body Effects and Diversity of Exciton States
journal, November 2013


Giant bandgap renormalization and excitonic effects in a monolayer transition metal dichalcogenide semiconductor
journal, August 2014


Probing excitonic dark states in single-layer tungsten disulphide
journal, August 2014


Exciton Binding Energy and Nonhydrogenic Rydberg Series in Monolayer WS 2
journal, August 2014


Fine structure of quantum well excitons
journal, January 1990


Exchange interaction and polariton effects in quantum-well excitons
journal, April 1990


Subpicosecond spin relaxation dynamics of excitons and free carriers in GaAs quantum wells
journal, December 1991


Exciton spin dynamics in quantum wells
journal, June 1993


Exciton dynamics in GaAs quantum wells under resonant excitation
journal, October 1994


Optical generation of excitonic valley coherence in monolayer WSe2
journal, August 2013


Direct measurement of exciton valley coherence in monolayer WSe2
journal, February 2016


Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides
journal, May 2014


Exciton band structure of monolayer MoS 2
journal, February 2015


Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS 2
journal, December 2013


Coherent Electronic Coupling in Atomically Thin MoSe 2
journal, May 2014


Tightly bound trions in monolayer MoS2
journal, December 2012


Two-dimensional spectroscopy of electronic couplings in photosynthesis
journal, March 2005


Long-lived quantum coherence in photosynthetic complexes at physiological temperature
journal, July 2010


Many-Body Interactions in Semiconductors Probed by Optical Two-Dimensional Fourier Transform Spectroscopy
journal, February 2006


Intrinsic homogeneous linewidth and broadening mechanisms of excitons in monolayer transition metal dichalcogenides
journal, September 2015


Excitonic luminescence upconversion in a two-dimensional semiconductor
journal, December 2015


Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2
journal, August 2015


BerkeleyGW: A massively parallel computer package for the calculation of the quasiparticle and optical properties of materials and nanostructures
journal, June 2012


QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials
journal, September 2009


Electron correlation in semiconductors and insulators: Band gaps and quasiparticle energies
journal, October 1986


Nonuniform sampling schemes of the Brillouin zone for many-electron perturbation-theory calculations in reduced dimensionality
journal, January 2017


wannier90: A tool for obtaining maximally-localised Wannier functions
journal, May 2008


Electron-Hole Excitations in Semiconductors and Insulators
journal, September 1998


Electron-hole excitations and optical spectra from first principles
journal, August 2000


From Bulk to Monolayer MoS2: Evolution of Raman Scattering
journal, January 2012


Sub-8-fs pulses from an ultrabroadband optical parametric amplifier in the visible
journal, January 1998


Pulse-front-matched optical parametric amplification for sub-10-fs pulse generation tunable in the visible and near infrared
journal, January 1998


Pulse-front matching of ultrabroadband near-infrared noncollinear optical parametric amplified pulses
journal, January 2009


Phase-stabilized two-dimensional electronic spectroscopy
journal, September 2004


Rapid and economical data acquisition in ultrafast frequency-resolved spectroscopy using choppers and a microcontroller
journal, January 2016


Room-Temperature Coherent Optical Phonon in 2D Electronic Spectra of CH 3 NH 3 PbI 3 Perovskite as a Possible Cooling Bottleneck
journal, June 2017