Electronic Band Tuning and Multivalley Raman Scattering in Monolayer Transition Metal Dichalcogenides at High...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spectroscopy

Background:

• Transition metal dichalcogenides (TMDs) exhibit spin-valley locking in K/K' valleys, with potential for phenomena involving Q/Q' valleys.
• Intervalley K-Q scattering is crucial for multivalley superconductivity but often hindered in monolayer TMDs by a large K-Q energy difference (ΔE_KQ).
• Reducing ΔE_KQ and probing valley dynamics are key to unlocking multivalley phenomena in 2D materials.

Purpose of the Study:

• To investigate the effect of high pressure on the electronic structure of monolayer MoS₂ and WSe₂.
• To probe K-Q valley crossing and multivalley scattering using double-resonance Raman (DRR) scattering.
• To establish DRR bands as sensitive probes for strain-induced electronic structure modifications in TMDs.

Main Methods:

• Application of high pressure to monolayer MoS₂ and WSe₂ samples.
• Utilizing double-resonance Raman (DRR) scattering to probe electronic properties and intervalley scattering.
• Complementary first-principles calculations and photoluminescence measurements.

Main Results:

• Observed pressure-induced enhancement of DRR LA and 2LA Raman bands in both MoS₂ and WSe₂.
• Attributed the enhancement to a pressure-induced band gap opening and a decrease in ΔE_KQ.
• Demonstrated the multivalley nature of DRR bands in WSe₂ and their sensitivity to strain.

Conclusions:

• DRR 2LA and LA bands serve as effective probes for strain-induced changes in TMD electronic structures.
• The intensity of these Raman bands can monitor compressive or tensile strain in TMDs.
• This work advances the understanding of multivalley phenomena, including superconductivity, valley coherence, and transport, in TMDs.