Microscopic view on Landau level broadening mechanisms in graphene

Funk, Hannah; Knorr, Andreas; Wendler, Florian; Malić, Ermin

doi:10.1103/physrevb.92.205428

Cited by 34 publications

(31 citation statements)

References 46 publications

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“…Here, we neglect the impact of carrier-carrier interaction on the LL dynamics since the occupations of only a small number of Landau levels around the Fermi energy are changed by low-energy terahertz radiation. Consequently, the energy-conserving carrier-carrier scattering channels are strongly suppressed by Pauli blocking [9,21]. We have verified the validity of this approximation by performing calculations with and without taking into account the Coulomb interaction in different regimes.…”

Section: A Semiconductor Bloch Equationsmentioning

confidence: 67%

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Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Wendler

Malić

2016

Phys. Rev. B

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We investigate the intraband carrier dynamics in Landau-quantized graphene after an optical excitation with low-energetic terahertz pulses. Based on a microscopic theory, we calculate time-dependent differential transmission spectra reflecting the Landau-level dynamics. Our calculations reveal a strong dependence on the Fermi energy E F of the graphene sample as well as on the applied magnetic field B. We find that the pump pulse can lead to both absorption bleaching and absorption enhancement depending on B and the position of E F with respect to the resonant Landau-level transition. As a result, positive and negative contributions in differential transmission spectra appear, in good agreement with recent pump-probe measurements.

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Section: A Semiconductor Bloch Equationsmentioning

confidence: 67%

“…1(a)]. This is further amplified by the fact that also the impurity-induced Landau-level broadening increases with the magnetic field [9,21,22].…”

Section: B Differential Transmission Spectrummentioning

confidence: 91%

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Wendler

Malić

2016

Phys. Rev. B

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“…The energy conservation of all interactions is softened due to the finite dephasing of coherences resulting in a broadening of LLs. The dephasing rates γ ll are determined self-consistently considering many-particle and impurity-induced scattering [23][24][25]. Details of the calculation including expressions for the pump and scattering rates, as well as the self-consistent determination of the dephasing rates can be found in the supplementary material.…”

Section: Microscopic Modellmentioning

confidence: 99%

Microscopic modeling of tunable graphene-based terahertz Landau-level lasers

2017

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In the presence of strong magnetic fields the electronic bandstructure of graphene drastically changes. The Dirac cone collapses into discrete non-equidistant Landau levels, which can be externally tuned by changing the magnetic field. In contrast to conventional materials, specific Landau levels are selectively addressable using circularly polarized light. Exploiting these unique properties, we propose the design of a tunable laser operating in the technologically promising terahertz spectral range. To uncover the many-particle physics behind the emission of light, we perform a fully quantum mechanical investigation of the non-equilibrium dynamics of electrons, phonons, and photons in optically pumped Landau-quantized graphene embedded into an optical cavity. The gained microscopic insights allow us to predict optimal experimental conditions to realize a technologically promising terahertz laser.The terahertz (THz) regime of the electromagnetic spectrum can be exploited in a wide range of applications including medical diagnostics, atmosphere and space science as well as security and information technology [1][2][3][4]. Although THz research has progressed significantly in the last 20 years, the transition from laboratory demonstration to practical environment has occurred slowly and only for some niche applications. The largest challenge is the lack of adequate, tunable THz radiation sources. In 1986, H. Aoki proposed to design Landau level (LL) lasers exploiting the discreteness of LLs in two-dimensional electron gases [5]. Here, the energetic LL spacing and thus the possible laser frequency can be externally tuned through the magnetic field. The challenge for the realization of such a laser is to obtain a stable population inversion, i.e. a larger carrier occupation within an energetically higher LL. Since conventional semiconductors exhibit an equidistant spectrum of LLs, strong Coulomb scattering acts in favor of an equilibrium Fermi-Dirac distribution and strongly counteracts the build-up of a population inversion. In contrast, graphene as a two-dimensional material with a linear dispersion exhibits a non-equidistant LL separation offering entirely different conditions for many-particle processes [6][7][8]. Exploiting these remarkable properties of Landauquantized graphene, we propose an experimentally accessible scenario to achieve continuous wave lasing with tunable frequencies in the technologically promising terahertz spectral regime. The non-equidistant arrangement of energy levels [9,10] combined with selection rules for circularly polarized light, allow to selectively address individual inter-LL * samuel.brem@physik.tu-berlin.de Figure 1. Laser scheme. Sketch of the energetically lowest Landau levels in graphene embedded in an optical cavity. (A) The linearly polarized optical pump field induces transitions l = −3 → +2 and l = −2 → +3 (yellow arrows), which results in a population inversion between l = +1 and l = +2 in the conduction band and l = −1 and l = −2 in the valance band.(B) The emission o...

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“…The shape of the Landau levels (LLs) in a disordered two-dimensional electronic system is important to many physical measurements, such as specific heat [1,2], magnetization [3], magnetocapacitance [4], and magnetoconductivity [5][6][7][8][9]. This subject has been theoretically and experimentally studied for many decades [10][11][12][13][14][15][16][17][18][19][20][21][22]. Based on the self-consistent Born approximation (SCBA), the shape of the lowest LL in the conventional two-dimensional electronic systems has been argued to be a semi-elliptical form, which is insensitive to the distribution of disorder [14].…”

Section: Introductionmentioning

confidence: 99%

Magnetic field independent shape of the zero-energy landau levels in a disordered T₃ model

Yang

Chen

et al. 2019

New J. Phys.

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Using the Lanczos recursion method, we exactly determine the shape of the zero-energy Landau level (LL) in a disordered T 3 lattice under a strong magnetic field. We discover that the shape of the zeroenergy LL depends on the distribution of disorder, but is independent of magnetic field strength. Our analytical study attributes this intriguing behavior to the macroscopic and magnetic field independent degeneracy owing to the existence of the flat band. Moreover, our simulations unravel that the density of states obeys an unconventional scaling law, leading to the fact that the relation between the magnetoconductivity and the carrier density is independent of the disorder strength.

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Microscopic view on Landau level broadening mechanisms in graphene

Cited by 34 publications

References 46 publications

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Microscopic modeling of tunable graphene-based terahertz Landau-level lasers

Magnetic field independent shape of the zero-energy landau levels in a disordered T₃ model

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Microscopic view on Landau level broadening mechanisms in graphene

Cited by 34 publications

References 46 publications

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Doping-dependent intraband carrier dynamics in Landau-quantized graphene

Microscopic modeling of tunable graphene-based terahertz Landau-level lasers

Magnetic field independent shape of the zero-energy landau levels in a disordered T3 model

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Magnetic field independent shape of the zero-energy landau levels in a disordered T₃ model