Theory of ultrafast spatio-temporal dynamics in semiconductor heterostructures

Knorr, Andreas; Hughes, S.; Stroucken, T.; Koch, S. W.

doi:10.1016/0301-0104(96)00120-6

Cited by 72 publications

(65 citation statements)

References 26 publications

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“…Having solved the Wannier equation for K À K, K À L and K À K 0 excitons, equation (1), and the Bloch equation, equation (2), we have access to the optical response of TMDs and can evaluate the radiative and non-radiative homogeneous linewidth of excitonic resonances to obtain the coherence lifetime of optically allowed excitons. Figure 2 illustrates the absorption spectrum of 2D sheets 36 of two representative monolayer TMDs including tungsten diselenide (WS 2 ) and molybdenum diselenide (MoSe 2 ). We predict the homogeneous linewidth of the energetically lowest lying A exciton to be in the range of a few meV corresponding to an excitonic coherence lifetime of a few hundreds of femtoseconds.…”

Section: Resultsmentioning

confidence: 99%

Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides

Selig

Berghäuser

Raja

et al. 2017

Ultrafast Phenomena and Nanophotonics XXI

155

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Atomically thin transition metal dichalcogenides are direct-gap semiconductors with strong light-matter and Coulomb interactions. The latter accounts for tightly bound excitons, which dominate their optical properties. Besides the optically accessible bright excitons, these systems exhibit a variety of dark excitonic states. They are not visible in the optical spectra, but can strongly influence the coherence lifetime and the linewidth of the emission from bright exciton states. Here, we investigate the microscopic origin of the excitonic coherence lifetime in two representative materials (WS 2 and MoSe 2 ) through a study combining microscopic theory with spectroscopic measurements. We show that the excitonic coherence lifetime is determined by phonon-induced intravalley scattering and intervalley scattering into dark excitonic states. In particular, in WS 2 , we identify exciton relaxation processes involving phonon emission into lower-lying dark states that are operative at all temperatures.

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Section: Resultsmentioning

confidence: 99%

Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides

Selig

Berghäuser

Raja

et al. 2017

Ultrafast Phenomena and Nanophotonics XXI

155

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“…6 and Supplementary Note 5). The theory is an extension of the methods developed previously by some of the authors 1,2,5,9,11,12,26,27 , and is extended in this work to rigorously include the effect of the time-dependent THz probe electric field. By selectively switching on and off the different scattering processes in the model, we find that the acoustic phonon modes have negligible contribution to the observed THz carrier dynamics on the timescale of tens of picoseconds; the observed dynamics are fully accounted for by the combined effect of carrier-optical-phonon scattering (which transfers energy from the carrier liquid to the lattice) and carrier-carrier scattering (which continuously rethermalizes the carrier population as highenergy carriers lose their energy to the lattice).…”

Section: Resultsmentioning

confidence: 99%

“…The explicit form of the many-particle contributions and the equation for the phonon dynamics can be found elsewhere 5,26,27 , for example, in ref. 5 in equations 22-24.…”

Section: Methodsmentioning

confidence: 99%

“…The experimental programme is complemented by the development of a theoretical model 26,27 based on the densitymatrix formalism that provides microscopic access to the timeand momentum-resolved dynamics of the carrier occupation, the phonon population for different optical and acoustic phonon modes, and the microscopic polarization determining the optical excitation of a disorder-free graphene system. An essential component of the theory is that it incorporates explicitly the time-dependent response of the system to the THz probe pulse; the macroscopic intraband current density induced by the THz probe, and hence the resulting dynamic THz response, is calculated by microscopically accounting for the full time-and momentum-dependent carrier-carrier and carrier-phonon interactions.…”

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confidence: 99%

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Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental carrier-carrier interactions and carrier-phonon relaxation processes in two-dimensional materials, and understanding of the physics underlying novel high-speed electronic and optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy and related techniques have interpreted the variety of observed signals within phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder. Here, we present an integrated experimental and theoretical programme, using ultrafast timeresolved terahertz spectroscopy combined with microscopic modelling, to systematically investigate the hot-carrier dynamics in a wide array of graphene samples having varying amounts of disorder and with either high or low doping levels. The theory reproduces the observed dynamics quantitatively without the need to invoke any fitting parameters, phenomenological models or extrinsic effects such as disorder. We demonstrate that the dynamics are dominated by the combined effect of efficient carrier-carrier scattering, which maintains a thermalized carrier distribution, and carrier-optical-phonon scattering, which removes energy from the carrier liquid.

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“…To microscopically model the dynamics of optically excited carriers in graphene, we have developed a theoretical approach based on the density matrix formalism [14][15][16][17]. The core of the approach is graphene Bloch equations allowing us to temporally and spectrally resolve the dynamics of electrons and phonons in different regimes [18,19].…”

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confidence: 99%

Experimentally accessible signatures of Auger scattering in graphene

2016

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The gapless and linear electronic band structure of graphene opens up Auger scattering channels bridging the valence and the conduction band and changing the charge carrier density. Here, we reveal experimentally accessible signatures of Auger scattering in optically excited graphene. To be able to focus on signatures of Auger scattering, we apply a low excitation energy, weak pump fluences, and a cryostatic temperature, so that all relevant processes lie energetically below the optical phonon threshold. In this regime, carrier-phonon scattering is strongly suppressed and Coulomb processes govern the carrier dynamics. Depending on the excitation regime, we find an accumulation or depletion of the carrier occupation close to the Dirac point. This reflects well the behavior predicted from Auger-dominated carrier dynamics. Based on this observation, we propose a multicolor pump-probe experiment to uncover the extreme importance of Auger channels for the nonequilibrium dynamics in graphene.

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Theory of ultrafast spatio-temporal dynamics in semiconductor heterostructures

Cited by 72 publications

References 26 publications

Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides

Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Experimentally accessible signatures of Auger scattering in graphene

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