Additional excitonic features and momentum-dark states in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ReS</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Avijit Dhara, Devarshi Chakrabarty, Poulami Das, Aswini K. Pattanayak, Sanjoy Paul, Subhrajit Mukherjee, Sajal Dhara
Abstract
Unidirectional in-plane structural anisotropy in rhenium-based dichalcogenides introduces a new class of 2D materials, exhibiting anisotropic optical properties. In this work, we perform temperature-dependent, polarization-resolved photoluminescence and reflectance measurements on several-layer ${\mathrm{ReS}}_{2}$. We discover two additional excitonic resonances (${\mathrm{X}}_{3}$ and ${\mathrm{X}}_{4}$), which can be attributed to the splitting of spin degenerate states. Strong in-plane oscillator strength of exciton species ${\mathrm{X}}_{1}$ and ${\mathrm{X}}_{2}$ is accompanied by weaker counterparts ${\mathrm{X}}_{3}$ and ${\mathrm{X}}_{4}$ with similar polarization orientations. The in-plane anisotropic dielectric function has been obtained for ${\mathrm{ReS}}_{2}$, which is essential for engineering light matter coupling for polarization-sensitive optoelectronic devices. Furthermore, our temperature-dependent study revealed the existence of low-lying momentum-forbidden dark states causing an anomalous PL intensity variation at 30 K, which has been elucidated using a rate equation model involving phonon scattering from these states. Our findings of the additional excitonic features and the momentum-dark states can shed light on the true nature of the electronic band structure of ${\mathrm{ReS}}_{2}$.