Abstract
The out-of-equilibrium Raman response of graphene is addressed by pulsed laser excitation. Phonon spectrum is rationalized by revisiting the electron-phonon picture in the light of a transient broadening of the Dirac cone.
Highlights
Since its isolation in 2004 [1], graphene has been in focus of intense research activities, in view of its great potential to underpin new disruptive technologies, substituting materials used in existing applications and leading to radically new devices
We perform spontaneous Raman measurements in graphene by using a 3-ps laser pulses, which trade off between impulsive stimulation and sufficiently narrow excitation bandwidth for an adequate spectral resolution. This experimental strategy allows us to give insights about the role of e-ph coupling as relaxation channel in presence of an electronic temperature largely exceeding that of the phonon bath
Out-of-equilibrium ps-excitation regime reveals that a transient smearing out of the Dirac cones, determined by the photoinduced large electronic temperatures, opens additional intra-band relaxation channels for the e-ph coupling, while anharmonicity is ”frozen” at the negligible contribution pertaining to the much lower lattice temperature
Summary
Since its isolation in 2004 [1], graphene has been in focus of intense research activities, in view of its great potential to underpin new disruptive technologies, substituting materials used in existing applications and leading to radically new devices. Understanding the light-matter interaction processes, that characterize this gapless system, is critical to technological applications in diverse areas. For this purpose, over the last decade, non-equilibrium dynamics of charge carriers have generated great interest, leading to many theoretical and experimental studies [3]. Over the last decade, non-equilibrium dynamics of charge carriers have generated great interest, leading to many theoretical and experimental studies [3] Their main aim is to describe the different relaxation processes of the electrons (holes) in the conduction (valence) band, which can be conveniently excited by ultrashort pulsed laser. The interaction with pulsed light initially generates an out of equilibrium distribution of (hot) electrons with respect to the (cold) phonon bath. Relaxation to thermal equilibrium occurs within a few picoseconds through the fast electron-electron (e-e) and electronphonon (e-ph) non radiative recombination channels
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