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-doped two-dimensional semiconductor quantum wells
摘要： We present a theoretical study of photoabsorption in n-doped two-dimensional (2D) and quasi-2D semiconductors that takes into account the interaction of the photocreated exciton with Fermi-sea (FS) electrons through (i) Pauli blocking, (ii) Coulomb screening, and (iii) excitation of FS electron-hole pairs—that we here restrict to one. The system we tackle is thus made of one exciton plus zero or one FS electron-hole pair. At low doping, the system ground state is predominantly made of a 'trion-hole'—a trion (two opposite-spin electrons plus a valence hole) weakly bound to a FS hole—with a small exciton component. As the trion is poorly coupled to photon, the intensity of the lowest absorption peak is weak; it increases with doping, thanks to the growing exciton component, due to a larger coupling between two-particle and four-particle states. Under a further doping increase, the trion-hole complex is less bound because of Pauli blocking by FS electrons, and its energy increases. The lower peak then becomes predominantly due to an exciton dressed by FS electron-hole pairs, that is, an exciton-polaron. As a result, the absorption spectra of n-doped semiconductor quantum wells show two prominent peaks, the nature of the lowest peak turning from trion-hole to exciton-polaron under a doping increase. Our work also nails down the physical mechanism behind the increase with doping of the energy separation between the trion-hole peak and the exciton-polaron peak, even before the anticrossing, as experimentally observed.
关键词： Fermi sea,trion-hole complex,exciton-polaron,photoabsorption,Pauli blocking,n-doped semiconductors,Coulomb screening
更新于2025-09-23 15:23:52
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Three-particle electron-hole complexes in two-dimensional electron systems
摘要： Three-particle complexes consisting of two holes in the completely filled zero-electron Landau level and an excited electron in the unoccupied first Landau level are investigated in a quantum Hall insulator. The distinctive features of these three-particle complexes are an electron-hole mass symmetry and the small energy gap of the quantum Hall insulator itself. Theoretical calculations of the trion energy spectrum in a quantizing magnetic field predict that, besides the ground state, trions feature a hierarchy of excited bound states. In agreement with the theoretical simulations, we observe new photoluminescence lines related to the excited trion states. A relatively small energy gap allows the binding of three-particle complexes with magnetoplasma oscillations and the formation of plasmarons. The plasmaron properties are investigated experimentally.
关键词： photoluminescence,plasmarons,electron-hole mass symmetry,quantum Hall insulator,trion energy spectrum,three-particle complexes
更新于2025-09-23 15:21:01
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Many-particle excitations in non-covalently doped single-walled carbon nanotubes
摘要： Doping of single-walled carbon nanotubes leads to the formation of new energy levels which are able to participate in optical processes. Here, we investigate (6,5)-single walled carbon nanotubes doped in a solution of hydrochloric acid using optical absorption, photoluminescence, and pump-probe transient absorption techniques. We find that, beyond a certain level of doping, the optical spectra of such nanotubes exhibit the spectral features related to two doping-induced levels, which we assign to a localized exciton X and a trion T, appearing in addition to an ordinary exciton E1. We evaluate the formation and relaxation kinetics of respective states and demonstrate that the kinetics difference between E1 and X energy levels perfectly matches the kinetics of the state T. This original finding evidences the formation of trions through nonradiative relaxation via the X level, rather than via a direct optical excitation from the ground energy state of nanotubes.
关键词： exciton,doping,optical absorption,pump-probe transient absorption,photoluminescence,trion,single-walled carbon nanotubes
更新于2025-09-23 15:19:57
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Excitonic complexes in anisotropic atomically thin two-dimensional materials: Black phosphorus and
摘要： The effect of anisotropy in the energy spectrum on the binding energy and structural properties of excitons, trions, and biexcitons is investigated. To this end we employ the stochastic variational method with a correlated Gaussian basis. We present results for the binding energy of different excitonic complexes in black phosphorus (bP) and TiS3 and compare them with recent results in the literature when available, for which we find good agreement. The binding energies of excitonic complexes in bP are larger than those in TiS3. We calculate the different average interparticle distances in bP and TiS3 and show that excitonic complexes in bP are strongly anisotropic whereas in TiS3 they are almost isotropic, even though the constituent particles have an anisotropic energy spectrum. This is also confirmed by the correlation functions.
关键词： biexciton,TiS3,binding energy,black phosphorus,trion,anisotropy,stochastic variational method,exciton
更新于2025-09-09 09:28:46