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Frühere Veröffentlichungen
103. J. Lindlau, M. Selig, A. Neumann, L. Colombier, J. Kim, G. Berghäuser, F. Wang, E. Malic, A. Högele, "The role of momentum-dark excitons in the elementary optical response of bilayer WSe", Nature Comm. 9, 2586 (2018)
Monolayer transition metal dichalcogenides (TMDs) undergo substantial changes in the single-particle band structure and excitonic optical response upon the addition of just one layer. As opposed to the single-layer limit, the bandgap of bilayer (BL) TMD semiconductors is indirect which results in reduced photoluminescence with richly structured spectra that have eluded a detailed understanding to date. Here, we provide a closed interpretation of cryogenic emission from BL WSe2 as a representative material for the wider class of TMD semiconductors. By combining theoretical calculations with comprehensive spectroscopy experiments, we identify the crucial role of momentum-indirect excitons for the understanding of BL TMD emission. Our results shed light on the origin of quantum dot formation in BL crystals and will facilitate further advances directed at opto-electronic applications of layered TMD semiconductors in van der Waals heterostructures and devices.
Nature Comm. 9, 2586 (2018)102. G. Berghaeuser, I. Bernal-Villamil, R. Schmidt, R. Schneider, I. Niehues, P. Erhart, S. Michaelis de Vasconcellos, R. Bratschitsch, A. Knorr and E. Malic, "Inverted valley polarization in optically excited transition metal dichalcogenides", Nature Comm. 9, 971 (2018)
Large spin–orbit coupling in combination with circular dichroism allows access to spin-polarized and valley-polarized states in a controlled way in transition metal dichalcogenides. The promising application in spin-valleytronics devices requires a thorough understanding of intervalley coupling mechanisms, which determine the lifetime of spin and valley polarizations. Here we present a joint theory–experiment study shedding light on the Dexter-like intervalley coupling. We reveal that this mechanism couples A and B excitonic states in different valleys, giving rise to an efficient intervalley transfer of coherent exciton populations. We demonstrate that the valley polarization vanishes and is even inverted for A excitons, when the B exciton is resonantly excited and vice versa. Our theoretical findings are supported by energy-resolved and valley-resolved pump-probe experiments and also provide an explanation for the recently measured up-conversion in photoluminescence. The gained insights might help to develop strategies to overcome the intrinsic limit for spin and valley polarizations.
Nature Comm. 9, 971 (2018)101. A. Raja, M. Selig, G. Berghäuser, J. Yu, H. Hill, A. Rigosi, L. Brus, A. Knorr, T. Heinz, E. Malic and A. Chernikov, "Enhanced exciton-phonon scattering from monolayer to bilayer WS2", Nano Lett. 18, 6135 (2018)
Layered transition metal dichalcogenides exhibit the emergence of a direct bandgap at the monolayer limit along with pronounced excitonic effects. In these materials, interaction with phonons is the dominant mechanism that limits the exciton coherence lifetime. Exciton-phonon interaction also facilitates energy and momentum relaxation, and influences exciton diffusion under most experimental conditions. However, the fundamental changes in the exciton–phonon interaction are not well understood as the material undergoes the transition from a direct to an indirect bandgap semiconductor. Here, we address this question through optical spectroscopy and microscopic theory. In the experiment, we study room-temperature statistics of the exciton line width for a large number of mono- and bilayer WS2 samples. We observe a systematic increase in the room-temperature line width of the bilayer compared to the monolayer of 50 meV, corresponding to an additional scattering rate of ∼0.1 fs–1. We further address both phonon emission and absorption processes by examining the temperature dependence of the width of the exciton resonances. Using a theoretical approach based on many-body formalism, we are able to explain the experimental results and establish a microscopic framework for exciton–phonon interactions that can be applied to naturally occurring and artificially prepared multilayer structures.
Nano Lett. 18, 6135 (2018)100. I. Niehues, R. Schmidt, M. Drueppel, P. Marauhn, D. Christiansen, M. Selig, G. Berghäuser, D. Wigger, R. Schneider, L. Braasch, R. Koch, A. Castellanos-Gomez, T. Kuhn, A. Knorr, and E. Malic, M. Rohlfing, Michaelis de Vasconcellos, R. Bratschitsch, "Strain control of exciton-phonon coupling in atomically thin semiconductors", Nano Lett. 18, 1751 (2018)
Semiconducting transition metal dichalcogenide (TMDC) monolayers have exceptional physical properties. They show bright photoluminescence due to their unique band structure and absorb more than 10% of the light at their excitonic resonances despite their atomic thickness. At room temperature, the width of the exciton transitions is governed by the exciton–phonon interaction leading to strongly asymmetric line shapes. TMDC monolayers are also extremely flexible, sustaining mechanical strain of about 10% without breaking. The excitonic properties strongly depend on strain. For example, exciton energies of TMDC monolayers significantly redshift under uniaxial tensile strain. Here, we demonstrate that the width and the asymmetric line shape of excitonic resonances in TMDC monolayers can be controlled with applied strain. We measure photoluminescence and absorption spectra of the A exciton in monolayer MoSe2, WSe2, WS2, and MoS2 under uniaxial tensile strain. We find that the A exciton substantially narrows and becomes more symmetric for the selenium-based monolayer materials, while no change is observed for atomically thin WS2. For MoS2 monolayers, the line width increases. These effects are due to a modified exciton–phonon coupling at increasing strain levels because of changes in the electronic band structure of the respective monolayer materials. This interpretation based on steady-state experiments is corroborated by time-resolved photoluminescence measurements. Our results demonstrate that moderate strain values on the order of only 1% are already sufficient to globally tune the exciton–phonon interaction in TMDC monolayers and hold the promise for controlling the coupling on the nanoscale.
Nano Lett. 18, 1751 (2018)99. P. Steinleitner, P. Merkl, A. Graf, P. Nagler, C. Schueller, T. Korn, R. Huber, S. Brem, M. Selig, G. Berghaeuser, E. Malic "Dielectric engineering of electronic correlations in a van der Waals heterostructure", Nano Lett. 18, 1402 (2018)
Heterostructures of van der Waals bonded layered materials offer unique means to tailor dielectric screening with atomic-layer precision, opening a fertile field of fundamental research. The optical analyses used so far have relied on interband spectroscopy. Here we demonstrate how a capping layer of hexagonal boron nitride (hBN) renormalizes the internal structure of excitons in a WSe2 monolayer using intraband transitions. Ultrabroadband terahertz probes sensitively map out the full complex-valued mid-infrared conductivity of the heterostructure after optical injection of 1s A excitons. This approach allows us to trace the energies and line widths of the atom-like 1s–2p transition of optically bright and dark excitons as well as the densities of these quasiparticles. The excitonic resonance red shifts and narrows in the WSe2/hBN heterostructure compared to the bare monolayer. Furthermore, the ultrafast temporal evolution of the mid-infrared response function evidences the formation of optically dark excitons from an initial bright population. Our results provide key insight into the effect of nonlocal screening on electron–hole correlations and open new possibilities of dielectric engineering of van der Waals heterostructures.
Nano Lett. 18, 1402 (2018)98. G. Berghaeuser, P. Steinleitner, P. Merkl, R. Huber, A. Knorr and E. Malic, "Mapping of the dark exciton landscape in transition metal dichalcogenides", Phys. Rev. B, Rapid Comm. 98, 020301(R) (2018) Editor's Suggestion
Transition metal dichalcogenides (TMDs) exhibit a remarkable exciton physics including bright and optically forbidden dark excitonic states. Here, we show how dark excitons can be experimentally revealed by probing the intraexcitonic 1s−2p transition. Distinguishing the optical response shortly after the excitation and after the exciton thermalization allows us to reveal the relative position of bright and dark excitons. We find both in theory and experiment a clear blueshift in the optical response demonstrating the transition of bright exciton populations into lower-lying dark excitonic states.
Phys. Rev. B, Rapid Comm. 98, 020301(R) (2018) Editor's Suggestion97. S. Brem, F. Wendler, S. Winnerl and E. Malic, "Electrically pumped graphene-based Landau-level laser", Phys. Rev. Materials 2, 034002 (2018)
Graphene exhibits a nonequidistant Landau quantization with tunable Landau-level (LL) transitions in the technologically desired terahertz spectral range. Here, we present a strategy for an electrically driven terahertz laser based on Landau-quantized graphene as the gain medium. Performing microscopic modeling of the coupled electron, phonon, and photon dynamics in such a laser, we reveal that an inter-LL population inversion can be achieved resulting in the emission of coherent terahertz radiation. The presented paper provides a concrete recipe for the experimental realization of tunable graphene-based terahertz laser systems.
Phys. Rev. Materials 2, 034002 (2018)96. E. Malic, M. Selig, M. Feierabend, S. Brem, D. Christiansen, F. Wendler, A. Knorr, G. Berghaeuser, "Dark excitons in transition metal dichalcogenides", Phys. Rev. Materials 2, 014002 (2018)
Monolayer transition metal dichalcogenides (TMDs) exhibit a remarkably strong Coulomb interaction that manifests in tightly bound excitons. Due to the complex electronic band structure exhibiting several spin-split valleys in the conduction and valence band, dark excitonic states can be formed. They are inaccessibly by light due to the required spin-flip and/or momentum transfer. The relative position of these dark states with respect to the optically accessible bright excitons has a crucial impact on the emission efficiency of these materials and thus on their technological potential. Based on the solution of the Wannier equation, we present the excitonic landscape of the most studied TMD materials including the spectral position of momentum- and spin-forbidden excitonic states. We show that the knowledge of the electronic dispersion does not allow to conclude about the nature of the material's band gap since excitonic effects can give rise to significant changes. Furthermore, we reveal that an exponentially reduced photoluminescence yield does not necessarily reflect a transition from a direct to a nondirect gap material, but can be ascribed in most cases to a change of the relative spectral distance between bright and dark excitonic states.
Phys. Rev. Materials 2, 014002 (2018)95. M. Feierabend, G. Berghaeuser, M. Selig, S. Brem, T. Shegai, S. Eigler, E. Malic, "Molecule signatures in photoluminescence spectra of transition metal dichalcogenides", Phys. Rev. Materials 2, 014004 (2018)
Monolayer transition metal dichalcogenides (TMDs) show an optimal surface-to-volume ratio and are thus promising candidates for novel molecule sensor devices. It was recently predicted that a certain class of molecules exhibiting a large dipole moment can be detected through the activation of optically inaccessible (dark) excitonic states in absorption spectra of tungsten-based TMDs. In this paper, we investigate the molecule signatures in photoluminescence spectra in dependence of a number of different experimentally accessible quantities, such as excitation density, temperature, as well as molecular characteristics including the dipole moment and its orientation, molecule-TMD distance, molecular coverage, and distribution. We show that under certain optimal conditions even room-temperature detection of molecules can be achieved.
Phys. Rev. Materials 2, 014004 (2018)94. T. Mueller and E. Malic, "2D transition metal dichalcogenide semicondutors: exciton physics and devices", npj 2D Materials and Applications 2, 29 (2018)
Two-dimensional group-VI transition metal dichalcogenide semiconductors, such as MoS2, WSe2, and others, exhibit strong light-matter coupling and possess direct band gaps in the infrared and visible spectral regimes, making them potentially interesting candidates for various applications in optics and optoelectronics. Here, we review their optical and optoelectronic properties with emphasis on exciton physics and devices. As excitons are tightly bound in these materials and dominate the optical response even at room-temperature, their properties are examined in depth in the first part of this article. We discuss the remarkably versatile excitonic landscape, including bright, dark, localized and interlayer excitons. In the second part, we provide an overview on the progress in optoelectronic device applications, such as electrically driven light emitters, photovoltaic solar cells, photodetectors, and opto-valleytronic devices, again bearing in mind the prominent role of excitonic effects. We conclude with a brief discussion on challenges that remain to be addressed to exploit the full potential of transition metal dichalcogenide semiconductors in possible exciton-based applications.
npj 2D Materials and Applications 2, 29 (2018)93. S. Brem, G. Berghaeuser, M. Selig, E. Malic, "Exciton relaxation cascade in two-dimensional transition-metal dichalcogenides", Sci. Rep 8, 8238 (2018)
Monolayers of transition metal dichalcogenides (TMDs) are characterized by an extraordinarily strong Coulomb interaction giving rise to tightly bound excitons with binding energies of hundreds of meV. Excitons dominate the optical response as well as the ultrafast dynamics in TMDs. As a result, a microscopic understanding of exciton dynamics is the key for a technological application of these materials. In spite of this immense importance, elementary processes guiding the formation and relaxation of excitons after optical excitation of an electron-hole plasma has remained unexplored to a large extent. Here, we provide a fully quantum mechanical description of momentum- and energy-resolved exciton dynamics in monolayer molybdenum diselenide (MoSe2) including optical excitation, formation of excitons, radiative recombination as well as phonon-induced cascade-like relaxation down to the excitonic ground state. Based on the gained insights, we reveal experimentally measurable features in pump-probe spectra providing evidence for the exciton relaxation cascade.
Sci. Rep 8, 8238 (2018)92. M. Selig, G. Berghaeuser, M. Richter, R. Bratschitsch, A. Knorr and E. Malic, "Dark and bright exciton formation, thermalization and photoluminescence in monolayer TMDs", 2D Materials 5, 035017 (2018)
The remarkably strong Coulomb interaction in atomically thin transition metal dichalcogenides (TMDs) re-sults in an extraordinarily rich many-particle physics including the formation of tightly bound excitons. Besidesoptically accessible bright excitonic states, these materials also exhibit a variety of dark excitons. Since theycan even lie below the bright states, they have a strong influence on the exciton dynamics, lifetimes, and photo-luminescence. While very recently, the presence of dark excitonic states has been experimentally demonstrated,the origin of these states, their formation, and dynamics have not been revealed yet. Here, we present a mi-croscopic study shedding light on time- and energy-resolved formation and thermalization of bright and darkintra- and intervalley excitons as well as their impact on the photoluminescence in different TMD materials. Wedemonstrate that intervalley dark excitons, so far widely overlooked in current literature, play a crucial role intungsten-based TMDs giving rise to an enhanced photoluminescence and reduced exciton lifetimes at elevatedtemperatures.
2D Materials 5, 035017 (2018)91. I. Bernal-Villamil, G. Berghaeuser, M. Selig, I. Niehues, R. Schmidt, R. Schneider, P. Tonndorf, P. Erhart, S. Michaelis de Vasconcellos, R. Bratschitsch, A. Knorr and E. Malic, "Exciton broadening and band renormalization due to Dexter-like intervalley coupling", 2D Materials 5, 025011 (2018)
A remarkable property of atomically thin transition metal dichalcogenides (TMDs) is the possibility to selectively address single valleys by circularly polarized light. In the context of technological applications, it is very important to understand possible intervalley coupling mechanisms. Here, we show how the Dexter-like intervalley coupling mixes A and B states from opposite valleys leading to a significant broadening γB(1s) of the B1s exciton. The effect is much more pronounced in tungsten-based TMDs, where the coupling excitonic states are quasi-resonant. We calculate a ratio γB(1s)/γA(1s)≈4.0 , which is in good agreement with the experimentally measured value of 3.9±0.7. In addition to the broadening effect, the Dexter-like intervalley coupling also leads to a considerable energy renormalization resulting in an increased energetic distance between A1s and B1s states.
2D Materials 5, 025011 (2018)90. T. Winzer, M. Mittendorff, S. Winnerl, H. Mittenzwey, R. Jago, M. Helm, E. Malic and A. Knorr, "Unconventional double-bended saturation of optical transmission in graphene due to many-particle interaction", Nature Communications 8, 15042 (2017)
Saturation of carrier occupation in optically excited materials is a well-established phenomenon. However, so far, the observed saturation effects have always occurred in the strong-excitation regime and have been explained by Pauli blocking of the optically filled quantum states. On the basis of microscopic theory combined with ultrafast pump-probe experiments, we reveal a new low-intensity saturation regime in graphene that is purely based on many-particle scattering and not Pauli blocking. This results in an unconventional double-bended saturation behaviour: both bendings separately follow the standard saturation model exhibiting two saturation fluences; however, the corresponding fluences differ by three orders of magnitude and have different physical origin. Our results demonstrate that this new and unexpected behaviour can be ascribed to an interplay between time-dependent many-particle scattering and phase-space filling effects.
89. M. Feierabend, G. Berghaeuser, A. Knorr and E. Malic, "Proposal for dark exciton based chemical sensors", Nature Communications 8, 14776 (2017)
The rapidly increasing use of sensors throughout different research disciplines and the demand for more efficient devices with less power consumption depends critically on the emergence of new sensor materials and novel sensor concepts. Atomically thin transition metal dichalcogenides have a huge potential for sensor development within a wide range of applications. Their optimal surface-to-volume ratio combined with strong light–matter interaction results in a high sensitivity to changes in their surroundings. Here, we present a highly efficient sensing mechanism to detect molecules based on dark excitons in these materials. We show that the presence of molecules with a dipole moment transforms dark states into bright excitons, resulting in an additional pronounced peak in easy accessible optical spectra. This effect exhibits a huge potential for sensor applications, since it offers an unambiguous optical fingerprint for the detection of molecules—in contrast to common sensing schemes relying on small peak shifts and intensity changes.
88. D. Christiansen, M. Selig, G. Berghaeuser, R. Schmidt, I. Niehues, R. Schneider, A. Arora, S. Michaelis de Vasconcellos, R. Bratschitsch, E. Malic and A. Knorr, "Phonon Sidebands in Monolayer Transition Metal Dichalcogenides", Phys. Rev. Lett. 119, 187402 (2017)
Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.
Phys. Rev. Lett. 119, 187402 (2017)87. F. Wendler, M. Mittendorff, J. König-Otto, S. Brem, C. Berger, W. A. de Heer, R. Böttger, H. Schneider, M. Helm, S. Winnerl and E. Malic"Symmetry-breaking supercollisions in Landau-quantized graphene", Phys. Rev. Lett. 119, 067405 (2017)
Recent pump-probe experiments performed on graphene in a perpendicular magnetic field have revealedcarrier relaxation times ranging from picoseconds to nanoseconds depending on the quality of the sample.To explain this surprising behavior, we propose a novel symmetry-breaking defect-assisted relaxationchannel. This enables scattering of electrons with single out-of-plane phonons, which drastically acceleratethe carrier scattering time in low-quality samples. The gained insights provide a strategy for tuning thecarrier relaxation time in graphene and related materials by orders of magnitude.
86. R. Jago, F. Wendler, E. Malic, "Microscopic understanding of the photoconduction effect in graphene", Phys. Rev. B 96, 085431 (2017)
We investigate the photoresponse of intrinsic graphene in an in-plane electric field. Toward that end, we employ a microscopic approach that allows us to determine the time- and momentum-resolved charge-carrier distributions as a result of the interplay between the field-induced acceleration of optically excited carriers and Coulomb- and phonon-driven carrier scattering. Calculating the generated photocurrent that is determined by the asymmetry of the carrier distribution, we reveal the microscopic foundation of the photoconduction effect in graphene. In particular, we discuss the possibility of tuning the photocurrent via externally accessible knobs, such as electric field, temperature, and substrate. Furthermore, we study the impact of Auger-induced carrier multiplication on the photocurrent in graphene.
Phys. Rev. B 96, 085431 (2017)85. S. Brem, F. Wendler, E. Malic, "Microscopic modeling of tunable graphene-based terahertz Landau-level lasers", Phys. Rev. B 96, 045427 (2017)
In the presence of strong magnetic fields the electronic band structure of graphene drastically changes. The Dirac cone collapses into discrete nonequidistant 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 nonequilibrium dynamics of electrons, phonons, and photons in optically pumped Landau-quantized graphene embedded in a high-quality optical cavity. The microscopic insights gained allow us to predict optimal experimental conditions to realize a technologically promising terahertz laser.
84. M. Feierabend, A. Morlet, G. Berghaeuser, E. Malic, "Impact of strain on the optical fingerprint of monolayer transition metal dichalcogenides", Phys. Rev. B 96, 045425 (2017)
Strain presents a straightforward tool to tune electronic properties of atomically thin nanomaterials that are highly sensitive to lattice deformations. While the influence of strain on the electronic band structure has been intensively studied, there are only a few works on its impact on optical properties of monolayer transition-metal dichalcogenides (TMDs). Combining microscopic theory based on Wannier and Bloch equations with nearest-neighbor tight-binding approximation, we present an analytical view on how uni- and biaxial strain influences the optical fingerprint of TMDs, including their excitonic binding energy, oscillator strength, optical selection rules, and the radiative broadening of excitonic resonances. We show that the impact of strain can be reduced to changes in the lattice structure (geometric effect) and in the orbital functions (overlap effect). In particular, we demonstrate that the valley-selective optical selection rule is softened in the case of uniaxial strain due to the introduced asymmetry in the lattice structure. Furthermore, we reveal a considerable increase of the radiative dephasing due to strain-induced changes in the optical matrix element and the excitonic wave functions.
83. S. Aeschlimann, R. Krause, M. Chávez-Cervantes, H. Bromberger, R. Jago, E. Malic, A. Al-Temimy, C. Coletti, A. Cavalleri and I. Gierz, "Ultrafast momentum imaging of pseudospin-flip excitations in graphene", Phys. Rev. 96, 020301(R) (2017)
The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photoexcited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization and are maximum perpendicular to it. Here, we use time- and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy, and in-plane momentum. We first show that the rapidly-established quasithermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb- and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photoexcited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photocontrol experiments and optoelectronic device applications.
82. M. Feierabend, E. Malic, A. Knorr, and G. Berghaeuser, "Optical fingerprint of non-covalently functionalized transition metal dichalcogenides", J. Phys. Condens. Matter 29, 384003 (2017)
Atomically thin transition metal dichalcogenides (TMDs) hold promising potential for applications in opto-electronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibitefficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combinationwith circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials,they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach,where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we applythe density matrix theory to investigate the potential of non-covalently functionalized TMDs. Considering ex-emplary spiropyran molecules with a strong dipole moment, we predict spectral redshifts and the appearance ofan additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular char-acteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs,leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipolemoments open a channel for coherent intervalley coupling between the high-symmetry K and K’ points whichmay open new possibilities for spin-valleytronics application.
81. S. Winnerl, M. Mittendorff, J. König-Otto, H. Schneider, M. Helm, T. Winzer, A. Knorr and E. Malic, "Ultrafast processes in graphene: from fundamental manybody interactions to device applications", Annalen der Physik 1700022 (2017)
A joint experiment‐theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon energy (∼200 meV) and the Fermi energy (10‐20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon energy. Furthermore, a strongly anisotropic distribution of electrons in k‐space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non‐collinear Coulomb scattering. Finally, a room temperature operated ultra‐broadband hot‐electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40 ps.
Annalen der Physik 1700022 (2017)80. E. Malic, G. Berghaeuser, M. Feierabend and A. Knorr, "Optical response from functionalized atomically thin nanomaterials", Annalen der Physik 1700097 (2017)
Chemical functionalization of atomically thin nanostructures presents a promising strategy to create new hybrid nanomaterials with remarkable and externally controllable properties. Here, we review our research in the field of theoretical modeling of carbon nanotubes, graphene, and transition metal dichalcogenides located in molecular dipole fields. In particular, we provide a microscopic view on the change of the optical response of these technologically promising nanomaterials due to the presence of photo‐active spiropyran molecules. The feature article presents a review of recent theoretical work providing microscopic view on the optical response of chemically functionalized carbon nanotubes, graphene, and monolayered transition metal dichalcogenides. In particular, we propose a novel sensor mechanism based on the molecule‐induced activation of dark excitons. This results in a pronounced additional peak presenting an unambiguous optical fingerprint for the attached molecules.
Annalen der Physik 1700097 (2017)79. E. Malic, T. Winzer, F. Wendler, S. Brem, R. Jago, A. Knorr, M. Mittendorff, J. König-Otto, T. Plötzing, D. Neumaier, H. Schneider, M. Helm and S. Winnerl, "Carrier dynamics in graphene: ultrafast many-particle phenomena", Annalen der Physik, 1700038 (2017)
Graphene is an ideal material to study fundamental Coulomb‐ and phonon‐induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication ‐ an ultrafast many‐particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon‐induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene‐based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau‐quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion.
Annalen der Physik, 1700038 (2017)78. R. Jago, F. Wendler, E. Malic, "Current enhancement due to field-induced dark carrier multiplication in graphene", 2D Mater. 4, 021031 (2017)
We present a microscopic study on current generation in graphene in response to an electric field. While scattering is generally considered to reduce the current, we reveal that in graphene Auger processes give rise to a current enhancement via a phenomenon we denote dark carrier multiplication. Based on a microscopic approach, we show that, if other scattering channels are absent, this prevents the carrier distribution to reach a stationary value. Taking into account scattering with phonons a finite current is restored, however its value exceeds the stationary current without scattering.
2D Mater. 4, 021031 (2017)77. G. Berghäuser, A. Knorr and E. Malic, "Optical fingerprint of dark 2p-states in transition metal dichalcogenides", 2D Mater. 4, 015029 (2017)
Atomically thin transition metal dichalcogenides exhibit a remarkably strong Coulomb interaction. This results in a fascinating many-particle physics including a variety of bright and dark excitonic states that determine optical and electronic properties of these materials. So far, the impact of dark states has remained literally in the dark to a large extent, since a measurement of these optically forbidden states is very challenging. Here we demonstrate a strategy to measure a direct fingerprint of dark states even in standard linear absorption spectroscopy. We present a microscopic study on bright and dark higher excitonic states in the presence of disorder for the exemplary material of tungsten disulfide (WS2). We show that the geometric phase cancels the degeneration of 2s and 2p states and that a significant disorder-induced coupling of these bright and dark states offers a strategy to circumvent optical selection rules. As a proof, we show a clear fingerprint of dark 2p states in the absorption spectrum of WS2. The predicted softening of optical selection rules through exciton-disorder coupling is of general nature and therefore applicable to related two-dimensional semiconductors.
2D Mater. 4, 015029 (2017)76. M. Selig, G. Berghaeuser, A. Raja, P. Nagler, C. Schüller, T. F. Heinz, T. Korn, A. Chernikov, E. Malic and A. Knorr, "Excitonic linewidth and coherence lifetime in monolayer transition metal dichalcogenides", Nature Commun. 7, 13279 (2016)
Atomically thin transition metal dichalcogenides exhibit a remarkably strong Coulomb interaction. This results in a fascinating many-particle physics including a variety of bright and dark excitonic states that determine optical and electronic properties of these materials. So far, the impact of dark states has remained literally in the dark to a large extent, since a measurement of these optically forbidden states is very challenging. Here we demonstrate a strategy to measure a direct fingerprint of dark states even in standard linear absorption spectroscopy. We present a microscopic study on bright and dark higher excitonic states in the presence of disorder for the exemplary material of tungsten disulfide (WS2). We show that the geometric phase cancels the degeneration of 2s and 2p states and that a significant disorder-induced coupling of these bright and dark states offers a strategy to circumvent optical selection rules. As a proof, we show a clear fingerprint of dark 2p states in the absorption spectrum of WS2. The predicted softening of optical selection rules through exciton-disorder coupling is of general nature and therefore applicable to related two-dimensional semiconductors.
Nature Commun. 7, 13279 (2016)75. M. T. Mihnev, F. Kadi, C. J. Divin, T. Winzer, S. Lee, C. Liu, Z. Zhong, C. Berger, W. A. de Heer, E. Malic, A. Knorr and T. B. Norris, "Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene", Nature Commun. 7, 11617 (2016)
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 time-resolved 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.
Nature Commun. 7, 11617 (2016)74. R. Schmidt, G. Berghaeuser, R. Schneider, M. Selig, P. Tonndorf. E. Malic, A. Knorr, S. Michaelis de Vasconcellos and R. Bratschitsch, "Ultrafast Coulomb-induced intervalley coupling in atomically thin WS2", Nano Lett. 16, 2945 (2016)
Monolayers of semiconducting transition metal dichalcogenides hold the promise for a new paradigm in electronics by exploiting the valley degree of freedom in addition to charge and spin. For MoS2, WS2, and WSe2, valley polarization can be conveniently initialized and read out by circularly polarized light. However, the underlying microscopic processes governing valley polarization in these atomically thin equivalents of graphene are still not fully understood. Here, we present a joint experiment–theory study on the ultrafast time-resolved intervalley dynamics in monolayer WS2. Based on a microscopic theory, we reveal the many-particle mechanisms behind the observed spectral features. We show that Coulomb-induced intervalley coupling explains the immediate and prominent pump–probe signal in the unpumped valley and the seemingly low valley polarization degrees typically observed in pump–probe measurements compared to photoluminescence studies. The gained insights are also applicable to other light-emitting monolayer transition metal dichalcogenides, such as MoS2 and WSe2, where the Coulomb-induced intervalley coupling also determines the initial carrier dynamics.
Nano Lett. 16, 2945 (2016)73. T. Winzer, R. Jago and E. Malic, "Experimentally accessible signatures of Auger scattering in graphene", Phys. Rev. B 94, 235430 (2016)
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.
Phys. Rev. B 94, 235430 (2016)72. J. C. Koenig-Otto, M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm and S. Winnerl, "Slow non-collinear Coulomb scattering in the vicinity of the Dirac point in graphene", Phys. Rev. Lett. 117, 087401 (2016)
The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k directions pointing radially away from the Dirac point. Our study reveals, however, that, in almost intrinsic graphene, full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps time scale. This effect is very promising for infrared and THz devices based on hot carrier effects.
Phys. Rev. Lett. 117, 087401 (2016)71. E. Malic, T. Winzer, F. Wendler and A. Knorr, "Review on carrier multiplication in graphene", Phys. Status Solidi B 253, 2303 (2016)
The remarkable gapless and linear band structure of graphene opens up new carrier relaxation channels bridging the valence and the conduction band. These Auger scattering processes change the number of charge carriers and can give rise to a significant multiplication of optically excited carriers in graphene. This is an ultrafast many‐particle phenomenon that is of great interest both for fundamental many‐particle physics as well as technological applications. Here, we review the research on carrier multiplication in graphene and Landau‐quantized graphene including theoretical modeling and experimental demonstration.
Phys. Status Solidi B 253, 2303 (2016)70. F. Wendler and E. Malic, "Doping-dependent intraband carrier dynamics in Landau-quantized graphene", Phys. Rev. B 93, 035432 (2016)
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 EF 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 EF 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.
Phys. Rev. B 93, 035432 (2016)69. A. Singh, G. Moody, K. Tran, M. E. Scott, V. Overbeck, G. Berghäuser, J. Schaibley, E. J. Seifert, D. Pleskot, N. M. Gabor, J. Yan, D. G. Mandrus, M. Richter, E. Malic, X. Xu, and X. Li, "Trion formation dynamics in monolayer transition metal dichalcogenides", Phys. Rev. B 93, 041401(R) (2016)
We report charged exciton (trion) formation dynamics in doped monolayer transition metal dichalcogenides, specifically molybdenum diselenide (MoSe2), using resonant two-color pump-probe spectroscopy. When resonantly pumping the exciton transition, trions are generated on a picosecond time scale through exciton-electron interaction. As the pump energy is tuned from the high energy to low energy side of the inhomogeneously broadened exciton resonance, the trion formation time increases by ∼50%. This feature can be explained by the existence of both localized and delocalized excitons in a disordered potential and suggests the existence of an exciton mobility edge in transition metal dichalcogenides.
Phys. Rev. B 93, 041401(R) (2016)68. F. Kadi, T. Winzer, A. Knorr, and E. Malic, ”Impact of doping on the carrier dynamics in graphene”, Sci. Rep. 5, 16841 (2015)
67. H. Funk, F. Wendler, A. Knorr, and E. Malic, ”Microscopic view on Landau level broadening mechanisms in graphene”, Phys. Rev. B 92, 205428 (2015)
66. R. Jago, T. Winzer, and E. Malic, "Recombination channels in optically excited graphene", Phys. Status Solidi B 252, 2456 (2015)
65. F. Wendler, A. Knorr, and E. Malic, "Ultrafast carrier dynamics in Landau-quantized graphene", Nanophotonics 4, 224 (2015), review article
64. G. Moody, C. K. Dass, K. Hao, C.-H. Chen, L.-J. Li, A. Singh, K. Tran, G. Clark, X. Xu, G. Bergäuser, E. Malic, A. Knorr and X. Li,"Intrinsic Exciton Linewidth in Monolayer Transition Metal Dichalcogenides", Nature Commun. 6, 8315 (2015)
63. R. Jago, T. Winzer, A. Knorr, and E. Malic, "Graphene as Gain Medium for Broadband Lasers", Phys. Rev. B 92, 085407 (2015)
62. F. Wendler, and E. Malic, "Towards a tunable graphene-based Landau level laser in the terahertz regime", Sci. Rep. 5, 12646 (2015)
61. M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, P. Plochocka, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, "Carrier dynamics in Landau-quantized graphene featuring strong Auger scattering", Nature Phys. 11, 75 (2015)
60. T. Winzer, R. Ciesielski, M. Handloser, A. Comin, A. Hartschuh, E. Malic, "Microscopic view on the ultrafast photoluminescence from photo-excited graphene", Nano Lett. 15, 1141 (2015)
59. F. Wendler, A. Knorr and E. Malic, "Carrier multiplication in graphene under Landau quantization", Nature Commun. 5, 3703 (2014)
58. T. Plötzing, T. Winzer, E. Malic, D. Neumaier, A. Knorr, and H. Kurz,"Experimental verification of carrier multiplication in graphene", Nano Lett. 14, 5371 (2014)
57. M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, "Anisotropy of excitation and relaxation of photogenerated Dirac electrons in graphene", Nano Lett. 14, 1504 (2014)
56. F. Kadi, T. Winzer, E. Malic, A. Knorr, M. Mittendorff, S. Winnerl, F. Goettfert, and M. Helm,"Microscopic description of intraband absorption in graphene: the occurrence of transient negative differential transmission", Phys. Rev. Lett. 113, 035502 (2014)
55. G. Berghaeuser and E. Malic,"Molecule-substrate coupling in functionalized graphene", Carbon 69, 536 (2014)
54. E. Malic, H. Appel, O. T. Hofmann, A. Rubio, "Foerster-induced energy transfer in functionalized graphene", J. Phys. Chem C 118, 9283 (2014)
53. E. Malic, H. Appel, O. T. Hofmann, and A. Rubio, "Energy-transfer in porphyrin-functionalized graphene", Phys. Status Solidi B 251, 2495 (2014), highlighted on the cover of the issue
52. G. Berghaeuser and E. Malic, "Analytical approach to excitonic properties of MoS2", Phys. Rev. B 89, 125309 (2014)
51. F. Wendler and E. Malic, "Carrier-phonon scattering in Landau quantized graphene", Phys. Status Solidi B 251, 2541 (2014)
50. O. Dyatlova, C. Koehler, P. Vogel, E. Malic, R. Jain, K. Tvrdy, M. Strano, A. Knorr, and U. Woggon, "Relaxation dynamics of carbon nanotubes of enriched chiralities", Phys. Rev B 90, 155402 (2014)
49. F. Vialla, E. Malic, B. Langlois, Y. Chassagneux, C. Diederichs, E. Deleporte, P. Roussignol, J. S. Lauret, and C. Voisin, "Universal non- resonant absorption in carbon nanotubes", Phys. Rev. B 90, 155401 (2014)
48. F. Kadi and E. Malic, "Optical properties of Bernal-stacked bilayer graphene: A theoretical study", Phys. Rev. B 89, 045419 (2014)
47. F. Wendler, A. Knorr, and E. Malic, "Resonant carrier-phonon scattering in Landau-quantized graphene", Appl. Phys. Lett. 103, 253117 (2013)
46. G. Berghaeuser and E. Malic, "Optical properties of functionalized graphene", Phys. Status Solidi B 250, 2678 (2013)
45. T. Winzer and E. Malic, "The impact of pump fluence on carrier relaxation dynamics in optically excited graphene", J. Phys. Condens. Matter 25, 054201 (2013)
44. S. Winnerl, F. Göttfert, M. Mittendorff, H. Schneider, and M. Helm, T. Winzer, E. Malic, A. Knorr, M. Orlita, M. Potemski, M. Sprinkle, C. Berger, W. A. de Heer, "Time-resolved spectroscopy on epitaxial graphene in the infrared spectral range: relaxation dynamics and saturation behavior", J. Phys. Condens. Matter 25, 054202 (2013)
43. E. Verdenhalven, R. Binder, A. Knorr, and E. Malic, "Derivation of the screened Bloch equations and application to carbon nanostructures", J. Chem. Phys. 413, 3 (2013)
42. C. Köhler, T. Watermann, and E. Malic, "Time- and momentum-resolved phonon-induced relaxation dynamics in carbon nanotubes", J. Phys. Condens. Matter 25, 105301 (2013)
41. T. Winzer, E. Malic, and A. Knorr, "Microscopic mechanism for transient population inversion and optical gain in graphene", Phys. Rev. B 87, 165413 (2013)
40. E. Verdenhalven and E. Malic, "Excitonic absorption intensity of semiconducting and metallic carbon nanotubes", J. Phys. Condens. Matter 25, 245302 (2013)
39. O. A. Dyatlova, C. Köhler, E. Malic, J. Gomis-Bresco, J. Maultzsch, A. Tsagan-Mandzhiev, T. Watermann, A. Knorr, and U. Woggon, "Ultrafast Relaxation Dynamics via Acoustic Phonons in Carbon Nanotubes", Nano Lett. 12, 2249 (2012)
38. E. Malic, T. Winzer, and A. Knorr, "Efficient orientational carrier relaxation in optically excited graphene", Appl. Phys. Lett. 101, 213110 (2012)
37. T. Winzer, A. Knorr, M. Mittendorff, S. Winnerl, D. Sun, T. Norris, M. Helm, and E. Malic, "Absorption saturation in optically excited graphene", Appl. Phys. Lett. 101, 221115 (2012)
36. T. Winzer and E. Malic, "Impact of Auger processes on carrier dynamics in graphene", Phys. Rev. B Rapid Comm. 85, 241404(R) (2012)
35. D. Sun, C. Divin, M. Mihnev, T. Winzer, E. Malic, A. Knorr, J. E Sipe, C. Berger, W. A de Heer, P. N First, and T. B Norris, "Current relaxation due to hot carrier scattering in graphene", New J. Phys. 14, 105012 (2012)
34. E. Bobkin, A.Knorr, and E. Malic, "Exciton-phonon sidebands in metallic carbon nanotubes studied using semiconductor Bloch equations", Phys. Rev. B 85, 033409 (2012)
33. O. Dyatlova, J. Gomis-Bresco, E. Malic, H. Telg, J. Maultzsch, G. Zhong, J. Geng, and U. Woggon, "Dielectric screening effects on transition energies in aligned carbon nanotubes", Phys. Rev. B 85, 245449 (2012)
32. E. Malic, A. Setaro, P. Bluemmel, C. F. Sanz-Navarro, P. Ordejon, S. Reich, and A. Knorr, "Carbon nanotubes as substrates for molecular spiropyran-based switches", J. Phys. Cond. Matter 24, 394006 (2012)
31. C. Köhler, T. Watermann, and E. Malic, "Relaxation dynamics via acoustic phonons in carbon nanotubes", Phys. Status Solidi B 249, 2483 (2012)
30. E. Malic, C. Weber, M. Richter, V. Atalla, T. Klamroth, P. Saalfrank, S. Reich, and A. Knorr, "Microscopic model of the optical absorption of carbon nanotubes functionalized with molecular spiropyran photoswitches", Phys. Rev. Lett. 106, 097401 (2011)
29. S. Winnerl, M. Orlita, P. Plochocka, P. Kossacki, M. Potemski, T. Winzer, E. Malic, A. Knorr, M. Sprinkle, C. Berger, W. A. de Heer, H. Schneider, and M. Helm, "Carrier relaxation in epitaxial graphene photoexcited near the Dirac point", Phys. Rev. Lett. 107, 237401 (2011)
28. E. Malic, T. Winzer, E. Bobkin, and A. Knorr, "Microscopic theory of excitonic absorption and ultrafast many-particle kinetics in graphene", Phys. Rev. B 84, 205406 (2011)
27. M. Breusing, S. Kuehn, T. Winzer, E. Malic, F. Milde, N. Severin, J. P. Rabe, C. Ropers, A. Knorr, and T. Elsaesser, "Ultrafast nonequilibrium carrier dynamics in a single graphene layer", Phys. Rev. B. 83, 153410 (2011)
26. C. Köhler, A. Knorr, and E. Malic, "Microscopic study of temporally resolved carrier relaxation in carbon nanotubes", Phys. Rev. B 84, 153407 (2011)
25. J.-E. Kim, M.-R. Dachner, A. Wilms, M. Richter, and E. Malic, "Microscopic study of relaxation oscillations in quantum-dot VCSELs", Phot. Nano. Fund. Appl. 9, 337 (2011)
24. T. Winzer, and E. Malic, "Microscopic study of the efficiency of Coulomb- and phonon-induced relaxation channels in graphene", Phys. Status Solidi B 248, 2615 (2011)
23. E. Bobkin, and E. Malic, "Temperature dependence of exciton–phonon-induced sidebands in arbitrary carbon nanotubes", Phys. Status Solidi B 248, 2556 (2011)
22. T. Winzer, A. Knorr, and E. Malic, "Carrier Multiplication in Graphene", Nano Lett. 10, 4839 (2010), covered in the research news section of Solar Novus Today
21. E. Malic, J. Maultzsch, S. Reich, and A. Knorr, "Excitonic Rayleigh scattering spectra of metallic single-walled carbon nanotubes", Phys. Rev. B 82, 115439 (2010)
20. E. Malic, J. Maultzsch, S. Reich, and A. Knorr, "Excitonic absorption spectra of metallic single-walled carbon nanotubes", Phys. Rev. B 82, 035433 (2010)
19. E. Malic, M. Richter, J. Gomis-Bresco, U. Woggon, and A. Knorr, "Analytical Description of Gain Depletion an Recorvery in Quantum Dot Optical Amplifiers", New J. Phys. 12, 063012 (2010)
18. J.-E. Kim, E. Malic, M. Richter, and A. Knorr, "Maxwell-Bloch Equation Approach for Describing the Microscopic Dynamics of Quantum-Dot VCSELs", IEEE, J. Quantum Electron. 46 (2010)
17. M.-R. Dachner, E. Malic, M. Richter, A. Carmele, J. Kabuß, A. Wilms, J.-E. Kim, G. Hartmann, J. Wolters, U. Bandelow, and A. Knorr, "Theory of carrier and photon dynamics in quantum dot light emitters", Phys. Status Solidi B 247, 809 (2010)
16. E. Malic, M. Hirtschulz, S. Reich, and A. Knorr, "Excitonic absorption spectra and ultrafast relaxation dynamics in arbitrary carbon nanotubes", Phys. Status Solidi Rapid Res. Lett. 3, 196 (2009)
15. M. Hirtschulz, E. Malic, F. Milde, and A. Knorr, "Excitation induced dephasing and ultrafast intrasubband relaxation in carbon nanotubes", Phys. Rev. B 80, 085405 (2009)
14. E. Malic, M. Hirtschulz, J. Maultzsch, S. Reich, and A. Knorr, "Environmental influence on linear spectra and relaxation dynamics in carbon nanotubes'', Phys. Status Solidi B 246, 2592 (2009)
13. S. Heeg, E. Malic, C. Casiraghi, and S. Reich, "Quantitative composition of a SWCNT sample: Raman scattering vs. photoluminescence'', Phys. Status Solidi B 246, 2740 (2009)
12. J. Wolters, M.-R. Dachner, E. Malic, M. Richter, U. Woggon, and A. Knorr, "Carrier heating in light emitting quantum dot heterostructures caused by carrier phonon dynamics at low current injection", Phys. Rev. B 80, 245401 (2009)
11. J. Gomis-Bresco, S. Dommers, V. Temnov, U. Woggon, M. Lämmling, D. Bimberg, E. Malic, M. Richter, E. Schöll, and A. Knorr, "Impact of Coulomb Scattering on the Ultrafast Gain Recovery in InGaAs Quantum Dots", Phys. Rev. Lett. 101, 256803 (2008)
10. K. Lüdge, M. Bormann, E. Malic, P. Hövel, M. Kuntz, D. Bimberg, A. Knorr, and E. Schöll, "Turn-on dynamics and modulation response in semiconductor quantum dot lasers", Phys. Rev. B 78, 035316 (2008)
9. E. Malic, M. Hirtschulz, F. Milde, Y. Wu, J. Maultzsch, T. Heinz, A. Knorr, and S. Reich, "Theory of Rayleigh scattering from metallic carbon nanotubes", Phys Rev. B 77, 045432 (2008)
8. M. Hirtschulz, F. Milde, E. Malic, S. Butscher, C. Thomsen, S. Reich, and A. Knorr, "Carbon nanotube Bloch equations: a many-body approach to nonlinear and ultrafast optical properties", Phys. Rev. B 77, 035403(2008)
7. E. Malic, M. Hirtschulz, F. Milde, M. Richter, J. Maultzsch, S. Reich, and A. Knorr, "Coulomb effects in single-walled carbon nanotubes", Phys. Status Solidi B 245, 2155 (2008)
6. M. Hirtschulz, F. Milde, E. Malic, C. Thomsen, S. Reich, and A. Knorr, "Theory of ultrafast intraband relaxations in carbon nanotubes", Phys. Status Solidi B 245, 2164 (2008)
5. S. Butscher, F. Milde, M. Hirtschulz, E. Malic, and A. Knorr "Hot Electron Relaxation and Phonon Dynamics in Graphene", Appl. Phys. Lett. 91, 203103 (2007)
4. E. Malic, M. J. P. Bormann, P. Hövel, M. Kuntz, D. Bimberg, A. Knorr, and E. Schöll, "Coulomb damped relaxation oscillations in semiconductor quantum dot lasers", IEEE, J. Sel. Topics Quantum Electron. 13, 1242 (2007)
3. E. Malic, M. Hirtschulz, F. Milde, Y. Wu, J. Maultzsch, T. Heinz, A. Knorr, and S. Reich, " Theoretical approach to Rayleigh and absorption spectra of semiconducting carbon nanotubes", Phys. Status Solidi B, 244, 4240 (2007)
2. E. Malic, M. Hirtschulz, F. Milde, A. Knorr, and S. Reich "Analytical approach to optical properties of carbon nanotubes", Phys. Rev. B 74,195431 (2006)
1. E. Malic, K. J. Ahn, M. J. P. Bormann, P. Hövel, E. Schöll, A. Knorr, M. Kuntz, and D. Bimberg "Theory of relaxation oscillations in semiconductor quantum dot lasers", Appl. Phys. Lett. 89, 101107 (2006)