Phonon-mediated shift currents in twisted bilayer MoS2

Twisted bilayer molybdenum disulfide (MoS2) exhibits significant bulk photovoltaic effects (BPVE) due to its unique moiré superlattice, which introduces nontrivial quantum geometry and modulates the electronic bands. Here, we investigate the mechanisms underlying the BPVE in twisted bilayer MoS2, focusing on the role of phonon-assisted processes. We find that phonon-assisted transitions can mediate a non-zero displacement of electron and hole wave packets, a critical component of shift current. This displacement, driven by the interband Berry connection, leads to a measurable change in the polarization phase of the shift current. Using laser excitation at different wavelengths, we observe variations in the polarization phase during interband excitonic transitions, highlighting the critical role of phonons. Our findings reveal phonon-mediated interband processes and modulation mechanisms of shift vectors, which provide design principles for developing twist-engineered optoelectronic devices with polarization-programmable photoresponse.