Direct Measurement of Mode-resolved Electron-Phonon Coupling with Two-Dimensional Spectroscopy

Electron-phonon coupling (EPC) is foundational in condensed matter physics, determining intriguing phenomena and properties in both conventional and quantum materials. In this manuscript, we propose and demonstrate a novel two dimensional (2D) EPC spectroscopy which allows for direct extraction of EPC matrix elements. We find that two pronounced phonon modes of methylammonium lead iodide (MAPI) at room temperature exhibit highly distinctive EPC behaviors, both in strength, geometry, and temperature dependence across the phase transition. This demonstration indicates the potential of our novel 2D spectroscopy for studying the evolution of mode-resolved EPC at various external conditions and phonon-mediated light induced ultrafast control of condensed materials.