Mechanical Detuning of Exciton-Phonon Resonance in WS2

TL;DR

This study demonstrates that mechanical strain can effectively tune exciton-phonon interactions in WS2, enabling reversible control of resonance conditions in Raman scattering without changing the excitation energy.

Contribution

It introduces a method to mechanically induce excitonic resonance shifts in WS2, providing a new way to control light-matter interactions in 2D semiconductors.

Findings

Biaxial strain up to 1.3% shifts B exciton by 180 meV

Resonance conditions can be controlled mechanically, affecting Raman modes

First-order phonons remain stable and reversible under strain

Abstract

Controlling resonant Raman scattering in two-dimensional semiconductors typically requires tuning the excitation energy to match excitonic transitions. Here we show that mechanical deformation can achieve the same effect without changing the laser energy, enabling a controlled transition between resonant and non-resonant Raman scattering at fixed excitation. By applying biaxial strain up to 1.3% to WS2, the B exciton is red-shifted by 180 meV. This large excitonic shift leads to a pronounced collapse of the double-resonant 2LA(M) mode under 532 nm excitation, quantitatively described by a resonance model formulated in terms of the B exciton energy. Meanwhile, first-order phonons remain narrow and reversible, confirming elastic deformation and efficient strain transfer. These results establish mechanical strain as an effective knob to control exciton-phonon mediated light-matter interactions. They enable deterministic and reversible tuning of resonance-enhanced Raman scattering and excitonic optical responses in layered semiconductors.