Search results for "Polaron"
showing 10 items of 79 documents
Coherent and incoherent phonon processes in artificial atoms
2003
Carrier-phonon interaction in semiconductor quantum dots leads to three classes of phenomena: coherent effects (spectrum reconstruction) due to the nearly-dispersionless LO phonons, incoherent effects (transitions) induced by acoustical phonons and dressing phenomena, related to non-adiabatic, sub-picosecond excitation. Polaron spectra, relaxation times and dressing-related decoherence rates are calculated, in accordance with experiment.
Theoretical analysis of hole self-trapping in ionic solids: Application to the KCl crystal.
1993
A method for the calculation of the hole self-trapping (ST) energy in ionic crystals is proposed. It combines model-Hamiltonian and quantum-chemical approaches. An artificial path for the ST process has been suggested containing (a) a free hole not interacting with the lattice vibrations; (b) a free-hole wave packet localized in a small crystal volume in the form of the real ST state, all crystal ions being in their perfect lattice positions; (c) the final ST state of the hole, accompanied with a corresponding lattice relaxation, including strong displacements of ions belonging to the hole region. Some intermediate states might be adopted between (a) and (b) in order to simplify the calcula…
Use of site symmetry in supercell models of defective crystals: Polarons in CeO2
2017
The authors thank R. Merkle and G. W. Watson for stimulating discussions. E. K. also acknowledges partial financial support from the Russian Science Foundation for the study of charged defects under the project 14-43-00052. A. C. also acknowledges financial support from the University of Latvia Foundation (Arnis Riekstins's "MikroTik" donation). E. K. and D. G. express their gratitude to the High Performance Computer Centre in Stuttgart (HLRS, project DEFTD 12939) for the provided computer facilities whereas R. A. E. thanks the St. Petersburg State University Computer Center for assistance in high-performance calculations.
Computer Modeling of Luminescence in ABO3 Perovskites
2001
ABSTRACTWe suggest theoretical interpretation to a long-debated discussion on a nature of the intrinsic “green” luminescence observed in many ABO3 perovskites. For this purpose we performed quantum chemical calculations using the Intermediate Neglect of the Differential Overlap combined with the Large Unit Cell periodic model. Triplet exciton which is very likely responsible for the “green” luminescence is shown to be in a good approximation a pair of nearest Jahn-Teller electron and hole polarons (a bipolaron).
Quantum-chemical simulations of free and bound hole polarons in corundum crystal
1997
Abstract The semi-empirical method of the so-called intermediate neglect of differential overlap (INDO) has been applied to the calculations of the hole small-radius polarons in corundum crystals. Results for optimized atomic and electronic structure using two different approaches (the molecular cluster and periodic, supercell model) are critically compared. It is shown that the main results are similar in both cases.
Mollwo–Ivey relations for optical absorption bands of the atomic and F′ centres in alkali halides
2001
Evidence indicates that two classes of the transient IR-absorption bands: (a) with maxima at 0.27-0.36 eV in NaCI, KCI, KBr, KI and RbCl and due to shallow electron traps or bound polarons according to Jacobs (Phys. Stat. Sol. B 129 (1985) 755) and Korovkin and Lebedkina (Fiz. Tverd. Tela (Russian) 35 (1993) 642), and (b) with maxima at 0.15-0.36 eV in NaI, NaBr, NaCl : I, KCl : I I, RbCl: I and RbBr : I, due to on-centre STE localised at iodine-dimer according to Hirota et al. (J. Phys. Soc. Japan 63 (1994) 2774, Phys. Rev. B 52 (1995) 7779) and Edamatsu and Hirai (Mater. Sci. Forum 239-241 (1997) 525), are caused by the same defect. We propose that the defect is an atomic alkali impurity …
Anharmonicity-induced polaron relaxation in GaAs/InAs quantum dots
2002
The anharmonicity-induced relaxation of a polaron in a quantum dot is analyzed using the Davydov diagonalization method, including the coherent renormalization of the relevant third-order phonon interaction. The resulting relaxation time for a small GaAs/InAs self-assembled quantum dot turns out to be a few times longer than that found previously by a perturbative method.
Effect of disorder produced by cationic vacancies at theBsites on the electronic properties of mixed valence manganites
1999
An alloy series of single-phased polycrystalline ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Na}}_{x}{\mathrm{MnO}}_{3+\mathrm{\ensuremath{\delta}}} (0l~xl~0.15)$ has been synthesized in order to study the effect of disorder on the electronic properties of mixed valence manganites. The synthetic variables allow one to maintain a constant proportion of ${\mathrm{Mn}}^{4+}$ in the samples $({\mathrm{Mn}}^{3+}{/\mathrm{M}\mathrm{n}}^{4+}=2.1\ifmmode\pm\else\textpm\fi{}0.2),$ while the similar size of ${\mathrm{La}}^{3+}$ and ${\mathrm{Na}}^{+}$ ions results in no appreciable change in the tolerance factor of the perovskite structure throughout the series. In this way, the sodium content x contro…
Tunable Polarons in Bose-Einstein Condensates
2017
A toolbox for the quantum simulation of polarons in ultracold atoms is presented. Motivated by the impressive experimental advances in the area of ultracold atomic mixtures, we theoretically study the problem of ultracold atomic impurities immersed in a Bose-Einstein condensate mixture (BEC). The coupling between impurity and BEC gives rise to the formation of polarons whose mutual interaction can be effectively tuned using an external laser driving a quasi-resonant Raman transition between the BEC components. Our scheme allows one to change the effective interactions between polarons in different sites from attractive to zero. This is achieved by simply changing the intensity and the frequ…
Density of States characterization of TiO2 films deposited by Pulsed Laser Deposition for Heterojunction solar cells
2021
The application of titanium dioxide (TiO2) in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells with the role of electron selective contact. For modeling-based optimization of such contact, knowledge of the titanium oxide defect density of states is crucial. In this paper, we report a method to extract the defect density through nondestructive optical measures, including the contribution given by small polaron optical transitions. The presence of both related to oxygen-vacancy defects and polarons is supported by the results of optical characterizations and the evaluation of previous observations resulting in a defect band …