Strong coupling between a dielectric nanocavity and a monolayer transition metal dichalcogenide

We demonstrate strong coupling between light in a dielectric nanocavity with deep subwavelength confinement and excitons in a monolayer of molybdenum ditelluride. Avoided crossing is demonstrated by both photoluminescence and reflection measurements, from which we extract a light-matter interaction strength of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi>g</a:mi> <a:mi>PL</a:mi> </a:msub> <a:mo>=</a:mo> <a:mn>5.3</a:mn> <a:mo>±</a:mo> <a:mn>0.3</a:mn> <a:mspace width="0.16em"/> <a:mi mathvariant="normal">m</a:mi> <a:mi>eV</a:mi> </a:mrow> </a:math> and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msub> <d:mi>g</d:mi> <d:mi mathvariant="normal">R</d:mi> </d:msub> <d:mo>=</d:mo> <d:mn>4.7</d:mn> <d:mo>±</d:mo> <d:mn>0.7</d:mn> <d:mspace width="0.16em"/> <d:mi mathvariant="normal">m</d:mi> <d:mi>eV</d:mi> </d:mrow> </d:math> , respectively. The associated Rabi splitting is twice as large as the system's losses. These values are in good agreement with values obtained by an exciton reaction coordinate formalism, yielding <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mrow> <h:msub> <h:mi>g</h:mi> <h:mi>theory</h:mi> </h:msub> <h:mo>=</h:mo> <h:mn>5.2</h:mn> <h:mo>±</h:mo> <h:mn>0.7</h:mn> <h:mspace width="0.16em"/> <h:mi mathvariant="normal">m</h:mi> <h:mi>eV</h:mi> </h:mrow> </h:math> . The strong light-matter interaction, combined with low losses and subwavelength confinement of light, demonstrates a regime of light-matter interactions where strong nonlinearities at the single-photon level are expected.