Fig. 3: Phonon modulates spectral region near d–d transition.
From: Magnetically brightened dark electron-phonon bound states in a van der Waals antiferromagnet
a Coherent phonon spectroscopy traces were obtained below the Néel temperature (77 K), with ~25 fs temporal resolution. The blue trace represents the energy integrated coherent phonon spectroscopy trace. The oscillatory part of the energy integrated transient reflectivity was extracted after subtracting an exponential background from the raw data. Energy integrated coherent phonon spectroscopy reveals three distinct high-frequency optical phonons at 5.2, 7.5, and 11.5 THz. The Fourier amplitudes of the oscillations are shown in the inset. The orange line represents the data obtained with a long pass filter (cut-off energy: 1.53 eV) that excludes the d–d level transition. This spectrally separates the spin–orbit-entangled exciton from d–d levels. The 7.5 THz phonon mode modulates the d–d transition region, whereas the region with excitons is not being modulated by this mode. b Energy-resolved coherent phonon spectroscopy. For finer energy resolution, the probe beam was sent to a monochromator and coherent phonon oscillations in the energy region between 1.46 and 1.62 eV, was measured. The data clearly shows that the modulations are mainly present in the spectral region near the d–d transition.
