Fig. 3: Two-phonon electron–phonon scatterings in mono- and bilayer WSe₂.

a, b Detailed dG/dV_b evolutions of positive (open brown circles) and negative (open blue squares) V_b in mono- (a) and bilayer (b) WSe₂ tunnel devices. The IETS spectra were taken at T = 0.45 K with an excitation voltage of V_pp = 0.3 mV. The lengths of the colored arrows, used for guiding the two-phonon excitations, represent the primary phonon energies in the monolayer WSe₂. c, d Simulated dG/dV_b spectra from quantum transport calculations for mono- (c) and bilayer (d) WSe₂ films. The single-phonon excitations are based on the monolayer data (Fig. 2b), and the two-phonon electron–phonon scatterings are from the composite two-phonon scattering routes regulated by layer-number dependent electronic band structures, inversion symmetries, and geometric phases. (insets, c, d) Schematic illustrations of two-phonon electron–phonon scattering routes at the K valley interacting with M and K phonons (c), and M and Q phonons (d).