Ultrafast Pseudospin Quantum Beats In Multilayer WSe2 And MoSe2 - Experimental Setup And Methods.pdf

Ultrafast Pseudospin Quantum Beats in Multilayer WSe2 and MoSe2

This document provides detailed supplementary information regarding the experimental methods, results, and discussions presented in the main paper titled "Ultrafast pseudospin quantum beats in multilayer WSe2 and MoSe2."

Experimental Setup (Figure S1):

- The experiment utilizes a mode-locked Ti:Sapphire laser producing 80 MHz pulses with a duration of approximately 80 fs.
- Laser pulses are split into two trains, focused onto the surface of TMDC (Transition Metal Dichalcogenide) samples using a plano convex lens.
- The sample is mounted in an optical cryostat with superconducting magnet coils for controlling external in-plane magnetic fields (B∥).
- Ellipticity of linearly polarized probe pulses, transmitted through the sample, is measured to analyze the temporal dynamics of valley polarization.

Sample Characterization (Figures S2 - S4):

- TRFE (Time-Resolved Faraday Ellipticity) measurements are performed on MoSe2 and WSe2 multilayer samples at various in-plane magnetic fields.
- The laser is tuned to excitonic absorption lines to induce valley polarization.
- Sharp spikes observed in the traces are measurement artifacts.
- Similar experiments are conducted for different exciton resonances (A1s and A2s) and magnetic field strengths.
- RC (Reabsorption Contrast) measurements using a white light source confirm the sample identities and quality.

Theoretical Modeling (Figure S5):

- Refractive index models, including background and Lorentzian oscillators for excitonic transitions, are used to fit the measured RC spectra.
- The number of complex Lorentz oscillators varies depending on the sample (see figure).
- Calculated g factors for a WSe2 bilayer align with trends observed in layer-dependent measurements.

Additional Sample (Figure S6):

- A large-area WSe2 bilayer encapsulated in hBN is prepared to further investigate out-of-plane g factors, consistent with previous layer-dependent measurements.