Title: Excitons in strained and suspended monolayer WSe₂

Abstract

Here, we study suspended membranes of atomically thin WSe₂ as hosts of excitons. We perform optical reflectance measurements to probe the exciton physics and obtain the peak energies for the 1$$s$$, 2$$s$$, and 3$$s$$ states of the $$A$$ exciton in suspended WSe₂ and consider supported membranes as a reference. We find that elimination of the influence of the dielectric environment enables a strong electron–hole interaction and a concomitant increase in the exciton binding energy in suspended monolayer (1L) WSe₂. Based on the experimental results, we calculate the excitonic binding energies by employing the recently developed quantum electrostatic heterostructure model and the commonly employed Rytova–Keldysh potential model. We see that the binding energy of the ground state $$A$$ exciton increases from about 0.3 eV (on a substrate) to above 0.4 eV (suspended). We also exploit the tunability of the excitons in suspended samples via mechanical strain. By applying external gas pressure of 2.72 atm to a 1L suspended over a circular hole of 8 μm diameter, we strain the WSe₂ and obtain a reversible 0.15 eV redshift in the exciton resonance. The linewidth of the $$A$$ exciton decreases by more than half, from about 50 to 20 meV under 1.5% biaxial strain at room temperature. This line narrowing is due to the suppression of intervalley exciton–phonon scattering. By making use of the observed strain-dependent optical signatures, we infer the two-dimensional (2D) elastic moduli of 1L and 2L WSe₂. Our results exemplify the use of suspended 2D materials as novel systems for fundamental studies, as well as for strong and dynamic tuning of their optical properties.

Authors:

Aslan, Burak  ^[1];

• Search DOE PAGES for author "Aslan, Burak"
• Search DOE PAGES for ORCID "0000-0002-0925-3026"

Yule, Colin ^[2]; Yu, Yifei ^[3]; Lee, Yan Joe ^[2]; Heinz, Tony F.  ^[2];

• Search DOE PAGES for author "Heinz, Tony F."
• Search DOE PAGES for ORCID "0000-0003-1365-9464"

Cao, Linyou ^[3]; Brongersma, Mark L.  ^[2]

• Search DOE PAGES for author "Brongersma, Mark L."
• Search DOE PAGES for ORCID "0000-0003-1777-8970"

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+ Show Author Affiliations

1. Stanford Univ., CA (United States); Bogazici Univ., Istanbul (Turkey)
2. Stanford Univ., CA (United States)
3. North Carolina State University, Raleigh, NC (United States)

Publication Date:

Thu Oct 21 00:00:00 EDT 2021

Research Org.:

Stanford Univ., CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC); National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR)

OSTI Identifier:

1979454

Grant/Contract Number:  

SC0019140; 1741693; FA9550-17-1-0002

Resource Type:

Accepted Manuscript

Journal Name:

2D Materials

Additional Journal Information:

Journal Volume: 9; Journal Issue: 1; Journal ID: ISSN 2053-1583

Publisher:

IOP Publishing

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; WSe₂; exciton binding energy; dielectric screening; suspended monolayer; bilayer