Time-Resolved Raman Scattering in Exfoliated and CVD Graphene Crystals

Katsiaounis, Stavros; Paterakis, Georgios; Sharkov, A. V.; Papagelis, Konstantinos; Parthenios, John; Khoroshilov, Eugeniy V.

doi:10.1021/acs.jpcc.1c05469

Cited by 8 publications

(2 citation statements)

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“…Electron–phonon coupling (EPC) plays a crucial role in the aforesaid ultrafast phenomena, ,− and thus, it is of utmost importance to master and comprehend microscopic channels governing phonon dynamics in extreme nonequilibrium conditions. Complementary to the time-resolved photoemission methods that provide an important access to the electron–hole thermalization process ,,− and electronic structure changes, , there are several ultrafast techniques, such as ultrafast electron diffraction scattering, − coherent phonon spectroscopy, − and time-resolved Raman spectroscopy, − that can precisely track the phonon relaxation channels following the photoexcitation and corresponding EPC strength. , For instance, ultrafast electron diffraction had uncovered highly anisotropic non-thermal phonon relaxation in black phosphorus and mapped momentum-resolved electron–phonon scattering channels and strengths in various transition-metal dichalcogenides (TMDs). ,,, Intriguingly, these methods are able to analyze photo-induced phonon frequency modifications and uncover the relevant microscopic processes, as it was done, for example, for zone-center strongly coupled E 2g optical mode in graphite with coherent phonon and time-resolved Raman spectroscopies, as well as for the amplitude CDW mode in TiSe 2 by means of ultrafast electron diffraction . In combination with other time-resolved spectroscopy approaches, the latter technique allowed us to pinpoint the phonon modes that play an active role in unconventional superconductivity of FeSe thin films on SrTiO 3 and to extract the correlation-induced EPC constants .…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Nonadiabatic Phonon Renormalization in Photoexcited Single-Layer MoS₂

2023

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Comprehending nonequilibrium electron−phonon dynamics at the microscopic level and at short time scales is one of the main goals in condensed matter physics. Effective temperature models and time-dependent Boltzmann equations are standard techniques for exploring and understanding the nonequilibrium state and the corresponding scattering channels. However, these methods consider only the time evolution of the carrier occupation function, while the self-consistent phonon dressing in each time instant coming from the nonequilibrium population is ignored, which makes them less suitable for studying ultrafast phenomena where softening of the phonon modes plays an active role. Here, we combine ab initio timedependent Boltzmann equations and many-body phonon self-energy calculations to investigate the full momentum-and mode-resolved nonadiabatic phonon renormalization picture in the MoS 2 monolayer under nonequilibrium conditions. Our results show that the nonequilibrium state of photoexcited MoS 2 is governed by the multi-valley topology of valence and conduction bands that brings about characteristic anisotropic electron−phonon thermalization paths and the corresponding phonon renormalization of strongly coupled modes around high-symmetry points of the Brillouin zone. As the carrier population is thermalized toward its equilibrium state, we track in time the evolution of the remarkable phonon anomalies induced by nonequilibrium and the overall enhancement of the phonon relaxation rates. This work shows potential guidelines to tailor the electron−phonon relaxation channels and control the phonon dynamics under extreme photoexcited conditions.

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Section: Introductionmentioning

confidence: 99%

Ultrafast Nonadiabatic Phonon Renormalization in Photoexcited Single-Layer MoS₂

2023

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“…The detection range starts from 50 cm -1 close to the 532 nm laser line, corresponding to phonon frequencies above 1.5 THz. Using a continuous-wave mode of the Raman laser instead of pulsed Raman probes used in usual time-resolved Raman spectroscopy techniques [10,11] allows to access to such very low energy vibrations.…”

Section: Introductionmentioning

confidence: 99%

Generation and Control of Coherent Terahertz Phonons in Silicon Metasurfaces

Martins

Petit

Brûlé

et al. 2022

Advanced Optical Materials

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free carrier creation and electron-phonon relaxations allowing the dissipation of the laser pulse energy into phonons. [6] For instance, Hudert and co-workers [7] demonstrated that femtosecond pulses are generating coherent acoustic phonons in silicon membranes, the latter phonons being detected by monitoring the changes of the dielectric constant in a pump probe experiment. In 1996, Hase and co-workers demonstrated that such coherent acoustic phonons, generated in a bismuth thin film, are interfering when generated by two delayed pulses. [8] Other experiments on thin films have demonstrated acoustic phonons propagation and reflections in layered media yielding to the determination of their velocity and their energy [7] and the fabrication of multilayered media or phononic crystals offers way of manipulating coherent acoustic phonons. [9] As such ultrafast lasers related techniques are offering a large avenue to study and control phonons at nanoscale in order to establish the design rules for future heat sinks at nanoscale. However, once miniaturization is pushed to its lower limit reaching, standard pump-probe reflection techniques relying on the detection of phonon wave propagation and reflection in thin films [7,8] are not relevant anymore when nanostructure dimensions are of the order of magnitude of optical wavelengths. Alternative approaches are required to investigate the phonons properties of acoustic phonon frequency.To address this bottleneck, we have implemented an alternative approach to probe high frequency phonons up to in the 1 to 20 THz range relying on inelastic scattering spectroscopy coupled to femtosecond pulses. Our approach allows to directly access to the acoustic phonon spectrum, which usually require to collect the time-dependent reflectivity Fourier transform. [7,8] Furthermore, we demonstrate that the temporal and spectral shaping of femtosecond pulses controls this coherent acoustic phonon emission spectrum in silicon metasurfaces.

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