TY - JOUR A1 - Tuan, Dinh Van A1 - Scharf, Benedikt A1 - Žutič, Igor A1 - Dery, Hanan T1 - Marrying excitons and plasmons in monolayer transition-metal dichalcogenides JF - Physical Review X N2 - Just as photons are the quanta of light, plasmons are the quanta of orchestrated charge-density oscillations in conducting media. Plasmon phenomena in normal metals, superconductors, and doped semiconductors are often driven by long-wavelength Coulomb interactions. However, in crystals whose Fermi surface is comprised of disconnected pockets in the Brillouin zone, collective electron excitations can also attain a shortwave component when electrons transition between these pockets. In this work, we show that the band structure of monolayer transition-metal dichalcogenides gives rise to an intriguing mechanism through which shortwave plasmons are paired up with excitons. The coupling elucidates the origin for the optical sideband that is observed repeatedly in monolayers of WSe\(_2\) and WS\(_2\) but not understood. The theory makes it clear why exciton-plasmon coupling has the right conditions to manifest itself distinctly only in the optical spectra of electron-doped tungsten-based monolayers. KW - physics KW - excitons KW - plasmons KW - semiconductors KW - spintronics KW - valleytronics Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-173030 VL - 7 IS - 4 ER - TY - JOUR A1 - Tempel, Jean-Sebastian A1 - Veit, Tempel A1 - Assmann, Marc A1 - Kreilkamp, Lars Erik A1 - Höfling, Sven A1 - Kamp, Martin A1 - Forchel, Alfred A1 - Bayer, Manfred T1 - Temperature dependence of pulsed polariton lasing in a GaAs microcavity JF - New Journal of Physics N2 - The second-order correlation function g\(^2\)(\(\tau\) = 0), input-output curves and pulse duration of the emission from a microcavity exciton-polariton system subsequent to picosecond-pulsed excitation are measured for different temperatures. At low temperatures a two-threshold behaviour emerges, which has been attributed to the onset of polariton lasing and conventional lasing at the first and the second threshold, respectively. We observe that polariton lasing is stable up to temperatures comparable with the exciton binding energy. At higher temperatures a single threshold displays the direct transition from thermal emission to photon lasing. KW - semiconductor microavity KW - quantized vortices KW - cavity polaritons KW - room temperature KW - excitons KW - time Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-134022 VL - 14 IS - 083014 ER - TY - JOUR A1 - Brüning, Christoph A1 - Wehner, Johannes A1 - Hausner, Julian A1 - Wenzel, Michael A1 - Engel, Volker T1 - Exciton dynamics in perturbed vibronic molecular aggregates JF - Structural Dynamics N2 - A site specific perturbation of a photo-excited molecular aggregate can lead to a localization of excitonic energy. We investigate this localization dynamics for laser-prepared excited states. Changing the parameters of the electric field significantly influences the exciton localization which offers the possibility for a selective control of this process. This is demonstrated for aggregates possessing a single vibrational degree of freedom per monomer unit. It is shown that the effects identified for the molecular dimer can be generalized to larger aggregates with a high density of vibronic states. KW - absorption spectra KW - excited states KW - polymers KW - excitons KW - wave functions Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-126085 VL - 3 ER - TY - JOUR A1 - Bieniek, Maciej A1 - Sadecka, Katarzyna A1 - Szulakowska, Ludmiła A1 - Hawrylak, Paweł T1 - Theory of excitons in atomically thin semiconductors: tight-binding approach JF - Nanomaterials N2 - Atomically thin semiconductors from the transition metal dichalcogenide family are materials in which the optical response is dominated by strongly bound excitonic complexes. Here, we present a theory of excitons in two-dimensional semiconductors using a tight-binding model of the electronic structure. In the first part, we review extensive literature on 2D van der Waals materials, with particular focus on their optical response from both experimental and theoretical points of view. In the second part, we discuss our ab initio calculations of the electronic structure of MoS\(_2\), representative of a wide class of materials, and review our minimal tight-binding model, which reproduces low-energy physics around the Fermi level and, at the same time, allows for the understanding of their electronic structure. Next, we describe how electron-hole pair excitations from the mean-field-level ground state are constructed. The electron–electron interactions mix the electron-hole pair excitations, resulting in excitonic wave functions and energies obtained by solving the Bethe–Salpeter equation. This is enabled by the efficient computation of the Coulomb matrix elements optimized for two-dimensional crystals. Next, we discuss non-local screening in various geometries usually used in experiments. We conclude with a discussion of the fine structure and excited excitonic spectra. In particular, we discuss the effect of band nesting on the exciton fine structure; Coulomb interactions; and the topology of the wave functions, screening and dielectric environment. Finally, we follow by adding another layer and discuss excitons in heterostructures built from two-dimensional semiconductors. KW - tight-binding KW - excitons KW - Bethe–Salpeter equation KW - transition metal dichalcogenides Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-275243 SN - 2079-4991 VL - 12 IS - 9 ER -