RESUMEN
Monolayer transition metal dichalcogenide semiconductors exhibit unique valleytronic properties interacting strongly with chiral phonons that break time-reversal symmetry. Here, we observed the ultrafast dynamics of linearly and circularly polarized E'(Γ) phonons at the Brillouin zone center in single-crystalline monolayer WS2, excited by intense, resonant, and polarization-tunable terahertz pulses and probed by time-resolved anti-Stokes Raman spectroscopy. We separated the coherent phonons producing directional sum-frequency generation from the incoherent phonon population emitting scattered photons. The longer incoherent population lifetime than what was expected from coherence lifetime indicates that inhomogeneous broadening and momentum scattering play important roles in phonon decoherence at room temperature. Meanwhile, the faster depolarization rate in circular bases than in linear bases suggests that the eigenstates are linearly polarized due to lattice anisotropy. Our results provide crucial information for improving the lifetime of chiral phonons in two-dimensional materials and potentially facilitate dynamic control of spin-orbital polarizations in quantum materials.
RESUMEN
Layered 2D halide perovskites with their alternating organic and inorganic atomic layers that form a self-assembled quantum well system are analogues of the purely inorganic 2D transition metal dichalcogenides. Within their periodic structures lie a hotbed of photophysical phenomena such as dielectric confinement effect, optical Stark effect, strong exciton-photon coupling, etc. Detailed understanding into the strong light-matter interactions in these hybrid organic-inorganic semiconductor systems remains modest. Herein, the intricate coherent interplay of exciton, spin, and phonon dynamics in (C6H5C2H4NH3)2PbI4 thin films using transient optical spectroscopy is explicated. New insights into the hotly debated origins of transient spectral features, relaxation pathways, ultrafast spin relaxation via exchange interaction, and strong coherent exciton-phonon coupling are revealed from the detailed phenomenological modeling. Importantly, this work unravels the complex interplay of spin-quasiparticle interactions in these layered 2D halide perovskites with large spin-orbit coupling.