Probing carrier dynamics in photo-excited graphene with time-resolved ARPES

Abstract

The dynamics of photo-generated electron-hole pairs in solids are dictated by many-body interactions such as electron-electron and electron-phonon scattering. Hence, understanding and controlling these scattering channels is crucial for many optoelectronic applications, ranging from light harvesting to optical amplification. Here we measure the formation and relaxation of the photo-generated non-thermal carrier distribution in monolayer graphene with time-and angleresolved photoemission spectroscopy. Using sub 10fs pulses we identify impact ionization as the primary scattering channel, which dominates the dynamics for the first 25fs after photo-excitation.Auger recombination is found to set in once the carriers have accumulated at the Dirac point with time scales between 100 and 250fs, depending on the number of non-thermal carriers. Our observations help in gauging graphene's potential as a solar cell and TeraHertz lasing material.

Dynamical properties of a driven dissipative dimerized S=12 chain

“…In general the spectrum of phonons covers the energy range from zero to the Debye energy,hω D , and hence 1/ω D sets the timescale for the decay of bath correlations. The Debye energy is typically 50-100 meV (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). For driving frequencies in the 1-10 THz regime and a decay rate, γ , which is 1/50 of these, it is clear that the correlation time scale, 1/ω D , is indeed shorter than the timescale 1/γ of the phonon damping (with the possible exception of very soft materials).…”

“…Laser facilities operating on the energy and ultrafast timescales of condensed-matter systems have been deployed recently to observe a wide array of novel phenomena in graphene [13], superconductors [14], charge-density-wave materials [15,16], and correlated insulators near their metallic transition [17,18]. Beyond inducing, enhancing, or destroying a symmetry-broken state, a key focus of these experiments has been the high-frequency Floquet regime, where steady laser driving can induce new topological states [19,20], the "time crystal" [21], or more generally allow the "Floquet engineering" of the electronic bands [22,23].…”

Photocarrier thermalization bottleneck in graphene

“…The photocarrier dynamics in graphene has been studied experimentally by means of pump-probe spectroscopy as well as time-and angle-resolved photoemission spectroscopy [8][9][10][11][12][13][14][15][16]. In the experiments the photoexcited carriers lie far above the Dirac point (by more than 1 eV), and the ultrafast relaxation of hot carriers is mainly attributed to optical phonon emission and carrier-carrier scattering, taking place within 150-170 fs [8,13].…”

Impact ionization dynamics in small band-gap two-dimensional materials from a coherent phonon mechanism

“…[1][2][3] This progress has facilitated the study of correlated and nanoscale quantum materials. [4] Besides graphene, [5][6][7][8][9] other two-dimensional materials, [10] in particular transition-metal dichalcogenides (TMDC), [11][12][13] have been the center of current investigations. Associated with this topic is an active interest in metal-insulator transitions.…”