Abstract
We present a flexible and efficient ultrafast time-resolved spontaneous Raman spectroscopy setup to study collective excitation and quasi-particle dynamics in quantum materials. The setup has a broad energy tuning range extending from the visible to near infrared spectral regions for both the pump excitation and Raman probe pulses. Additionally, the balance between energy and time-resolution can be controlled. A high light collecting efficiency is realized by high numerical aperture collection optics and a high-throughput flexible spectrometer. We demonstrate the functionality of the setup with a study of the zone-center longitudinal optical phonon and hole continuum dynamics in silicon and discuss the role of the Raman tensor in time-resolved Raman scattering. In addition, we show an evidence for unequal phonon softening rates at different high symmetry points in the Brillouin zone of silicon by means of detecting pump-induced changes in the two-phonon overtone spectrum. Demagnetization dynamics in the helimagnet Cu2OSeO3 is studied by observing softening and broadening of a magnon after photo-excitation, underlining the unique power of measuring transient dynamics in the frequency domain, and the feasibility to study phase transitions in quantum materials.
Highlights
The last decade has seen a surge of experiments where light is exploited as a strong external stimulus to manipulate quantum materials.1–3 The light-matter interaction can be a fully coherent process as in the case of the Floquet state in photon-dressed materials,4 or drive quantum materials into a strongly non-thermodynamic state by disturbance of the balance between electronic, orbital, spin, and lattice degrees of freedom
We have recently demonstrated in silicon that for a correct transient mode temperature determination a dynamical modification of the Raman tensor v2 needs to be taken into account
We have presented a flexible and efficient ultrafast time-resolved spontaneous Raman spectroscopy setup and illustrated its strength and capabilities with different conceptual time-resolved Raman studies of collective excitation and quasi-particle dynamics
Summary
The last decade has seen a surge of experiments where light is exploited as a strong external stimulus to manipulate quantum materials. The light-matter interaction can be a fully coherent process as in the case of the Floquet state in photon-dressed materials, or drive quantum materials into a strongly non-thermodynamic state by disturbance of the balance between electronic, orbital, spin, and lattice degrees of freedom. We show evidence for dissimilar electron-phonon scattering rates at different high symmetry points in the Brillouin zone (BZ) of silicon by detecting pump-induced changes in the two-phonon overtone spectrum This measurement underscores the unique resolving power of measuring transient changes in excitation energies in the frequency domain. With the high stability and sensitivity of the described setup, new avenues in ultrafast dynamical studies of quantum materials are foreseen These include the tracking of order parameter evolution and detection of symmetry changes across photo-induced phase transitions, the qualitative determination of energy and angular momentum transfer rates in the relaxation of non-equilibrium states, and time- and momentum-resolved scattering
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