[Paper Review] Atomically thin mirrors made of monolayer semiconductors

Giovanni Scuri, You Zhou+10 more|arXiv (Cornell University)|May 20, 2017

2D Materials and Applications49 references87 citations

TL;DR

A single MoSe2 monolayer, encapsulated by hexagonal boron nitride, acts as an electrically switchable mirror, reflecting up to 85% of incident light at cryogenic temperatures near the excitonic resonance.

ABSTRACT

Transition metal dichalcogenide monolayers are promising candidates for exploring new electronic and optical phenomena and for realizing atomically thin optoelectronic devices. They host tightly bound electron-hole pairs (excitons) that can be efficiently excited by resonant light fields. Here, we demonstrate that a single monolayer of molybdenum diselenide (MoSe2) can dramatically modify light transmission near the excitonic resonance, acting as an electrically switchable mirror that reflects up to 85% of incident light at cryogenic temperatures. This high reflectance is a direct consequence of the excellent coherence properties of excitons in this atomically thin semiconductor, encapsulated by hexagonal boron nitride. Furthermore, we show that the MoSe2 monolayer exhibits power- and wavelength-dependent nonlinearities that stem from exciton-based lattice heating in the case of continuous-wave excitation and exciton-exciton interactions when fast, pulsed laser excitation is used. These observations open up new possibilities for studying quantum nonlinear optical phenomena and topological photonics, and for miniaturizing optical devices.

Motivation & Objective

• Motivate exploration of exciton-coherent light-matter interactions in atomically thin semiconductors.
• Demonstrate that a MoSe2 monolayer can dramatically modify light transmission and reflectance near exciton resonance.
• Show power- and wavelength-dependent nonlinearities arising from exciton heating and exciton–exciton interactions.

Proposed method

• Use a single monolayer MoSe2 encapsulated in hexagonal boron nitride to preserve exciton coherence.
• Measure light transmission and reflection near the excitonic resonance at cryogenic temperatures.
• Probe continuous-wave excitation to observe lattice heating–related nonlinearities.
• Probe fast, pulsed laser excitation to observe exciton–exciton interaction–driven nonlinearities.

Experimental results

Research questions

• RQ1 Can a monolayer MoSe2 act as a tunable, atomically thin optical mirror near its excitonic resonance?
• RQ2 What are the roles of exciton coherence and encapsulation in achieving high reflectance?
• RQ3 What nonlinear optical phenomena arise in MoSe2 monolayers under continuous-wave versus pulsed excitation?
• RQ4 How do exciton-based processes enable potential applications in quantum nonlinear optics and topological photonics?

Key findings

• A MoSe2 monolayer can reflect up to 85% of incident light at cryogenic temperatures near the excitonic resonance.
• The high reflectance is due to the excellent coherence properties of excitons and encapsulation by hBN.
• Nonlinearities are power- and wavelength-dependent: lattice heating dominates under continuous-wave excitation, while exciton–exciton interactions dominate under fast pulsed excitation.
• Findings point to new possibilities for studying quantum nonlinear optical phenomena and miniaturizing optical devices.