Large Biaxial Compressive Strain Tuning of Neutral and Charged Excitons in Single-Layer Transition Metal Dichalcogenides

Abstract

The absorption and emission of light in single-layer transition metal dichalcogenides are governed by the formation of excitonic quasiparticles. Strain provides a powerful technique to tune the optoelectronic properties of two-dimensional materials and thus to adjust their exciton energies. The effects of large compressive strain in the optical spectrum of two-dimensional (2D) semiconductors remain rather unexplored compared to those of tensile strain, mainly due to experimental constraints. Here, we induced large, uniform, biaxial compressive strain (∼1.2%) by cooling, down to 10 K, single-layer WS 2 , MoS 2 , WSe 2 , and MoSe 2 deposited on polycarbonate substrates. We observed a significant strain-induced modulation of neutral exciton energies, with blue shifts up to 160 meV, larger than in any previous experiments. Our results indicate a remarkably efficient transfer of compressive strain, demonstrated by gauge factor values exceeding previous results and approaching theoretical expectations. At low temperatures, we investigated the effect of compressive strain on the resonances associated with the formation of charged excitons. In WS 2 , a notable reduction of gauge factors for charged compared to neutral excitons suggests an increase in their binding energy, which likely results from the effects of strain added to the influence of the polymeric substrate.

Modulation of the Superconducting Phase Transition in Multilayer 2H-NbSe2 Induced by Uniform Biaxial Compressive Strain

“…SiO 2 /Si-based and PC-based NbSe 2 devices are schematically depicted in Figure a and b, respectively. The large thermal expansion coefficient and Young’s modulus of polycarbonate makes it a suitable material for strain-transfer experiments with 2D materials. , Recently, the thermal compression and efficient strain transfer onto single-layer transition metal dichalcogenides (TMDs) has been quantified in a very low-temperature regime, making these substrates an interesting platform for studying the effects of large compressive strain in 2D materials at low temperatures. In fact, during the elaboration of this manuscript, KP Yip et al used a similar platform to subject a bulk (∼10 μm thick) layered superconductor, MoTe 2 , to homogeneous biaxial strain …”