Combined ultrafast spectroscopy techniques discloses the microscopic electron lattice interplay behind charge density waves

Understanding the complex interactions associated with charge, spin, lattice and orbital degrees of freedom is fundamental for emerging applications of quantum materials. In this context, ultrafast optical spectroscopy systems are promising tools to study the origin of complex orders. Here, an intense optical pulse brings the system out-of-equilibrium, providing an excellent opportunity to distinguish the dynamics of each subsystem. Using ultrafast techniques, we investigated charge density wave (CDW) behavior in transition-metal dichalcogenides (TMDs) after photo-excitation and during the relaxation time. To unravel the mechanisms underlying the correlations in CDW systems, we combined time resolved re ectivity (TRR) and time and angle resolved photoemission spectroscopy (TARPES). Our approach provides clear evidence of the phononic contribution to CDW phenomena in 1T-TiSe₂.