Phonon assisted absorption in Transition Metal Dichalcogenides heterostructures

Strong coupling between atomic motion and interlayer excitons in WSe₂/MoSe₂ heterojunction photodiodes have recently been observed in photocurrent measurements [1]. The vibronic states manifest as a palisade of pronounced periodic sidebands in the photocurrent spectrum in frequency windows close to the interlayer exciton resonances. These resonances occur periodically with an energy spacing of approximately 30 meV and are observed for two distinct interlayer excitons within the same heterostructure. This energy spacing corresponds to the frequency of a group of prominent phonon modes observed in the Raman spectrum of the heterostructure. We develop a model for the phonon assisted absorption where the low energy electronic excitations are coupled to the relevant phonon modes. By exploring the parameter space of phonon coupling strength, phonon energies, temperature, and electron-electron interaction we establish the design parameters where vibronic states are observable in optical absorption.





[1] Vibronic Exciton–Phonon States in Stack-Engineered van der Waals Heterojunction Photodiodes, Fatemeh Barati, Trevor B. Arp, Shanshan Su, Roger K. Lake, Vivek Aji, Rienk van Grondelle, Mark S. Rudner, Justin C. W. Song, and Nathaniel M. Gabor, Nano Lett. 2022, 22, 14, 5751–5758.