bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatially indirect photoluminescence of ZnSe/BeTe type II quantum wells in pulsed high magnetic fields
Authors: Takeyama Shojiro , Shen Rui , Enya Yohei , Kojima Eiji , Mino Hirofumi , Akimoto Ryoichi 
Published: October 2008

AbstractSpatially separated indirect photoemission in a non‐doped ZnSe/BeTe type II quantum structure is investigated by applying pulse magnetic field up to 50 T. The magnetic field dependences of the dichroic photoluminescence (PL) are well explained by an optical transition model associated with a positively charged exciton composed by an electron and two light holes. The PL is suppressed by magnetic field and also by temperature. Weak PL probably arising from localized excitons at interfaces is observed up to the highest magnetic field, and in high temperatures above 20 K. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Raman spectroscopy of charge‐ordered states in Magnéli titanium oxides
Authors: Watanabe Masayuki 
Published: October 2008

AbstractWe have systematically investigated the Raman spectra of the mixed‐valence compounds TinO2n–1 (n = 4,5,6) known as the Magnéli phases to elucidate the nature of the charge‐ordered states in these compounds. It is found that a stable charge‐ordered state exists only for Ti4O7. In the case of Ti5O9, the charge order is almost completely lost, and the charge order in Ti6O11 is incomplete. Thus each compound seems to be have quite individually. This result is unexpected in view of the similarity in the crystal structure. We interpret this seeming lack of the systematic trend as being due to the electron correlation effect which becomes less effective with increasing n. Also it is suggested that the charge order is unstable for the compounds with odd n. Finally the effects of temperature on the charge ordering in Ti5O9 and Ti6O11 are discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Collective effects of excitons with prominent retardation in multiple‐layered structures
Authors: Yasuda Hideki , Ishihara Hajime 
Published: October 2008

AbstractWe have investigated the collective excitonic effects in radiatively coupled thin layers by means of the transient pulse response theory. The degenerate four‐wave mixing (DFWM) signals show a strong dependence on the incident condition of the excitation pulses.Especially, when excitons in different layers are excited with prominent retardations compared to the pulse durations (that is, excitons in different layers are excited like dominoes), a huge variety of optical responses can occur, never seen in a usual simultaneous excitation of excitons. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy transfer to phonons after photoexcitation in one‐dimensional correlated electron‐phonon systems
Authors: Yonemitsu Kenji , Maeshima Nobuya 
Published: October 2008

AbstractIn order to study relaxation rates of photoexcited states in correlated electron systems, we calculate the time evolution of phonons' kinetic energies after photoexcitation of a one‐dimensional half‐filled Hubbard model coupled with different types of phonons, which modulate transfer integrals, site energies, and on‐site repulsion strengths. Without or with weak dimerization, the energy transfer to phonons that modulate on‐site repulsion strengths is the largest. It increases rapidly as a function of the corresponding displacement. This suggests that the rapid relaxation of photoexcited states in one‐dimensional correlated electron systems is allowed without change in symmetry by phonons that modulate Coulomb repulsion strengths. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Infrared transient absorption spectra for excited transition of excitons and biexcitons in CuCl
Authors: Yoshioka Takaaki , Miyajima Kensuke , Ashida Masaaki , Itoh Tadashi 
Published: October 2008

AbstractInfrared transient absorption (IRTA) spectra for excitons and biexcitons in CuCl bulk crystal have been measured by pump‐probe spectroscopy. The IRTA peak energy of the exciton agrees with the transition energy between Rydberg 1s to 2p states reported in one‐ and two‐photon absorption measurement. On the other hand, the IRTA peak energy of the biexcitons locates in energy higher than that of the excitons, which is reasonable by taking hydrogen molecule model into account. In addition, our results support the enhancement of the transition energy between 1s and 2p states in quantum dots compared to the bulk case. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Terahertz‐induced extreme nonlinear transients in semiconductor quantum wells
Authors: Lee Yun‐Shik , Danielson J. R. , Prineas J. P. , Steiner J. T. , Kira M. , Koch S. W. 
Published: October 2008

AbstractWe demonstrate terahertz‐induced extreme nonlinear transients in GaAs/AlGaAs quantum‐wells via terahertz‐pump and optical‐probe experiments. The light‐hole and heavy‐hole excitonic resonances exhibit strong spectral modulations that fluctuate on a subpicosecond time scale as the pump‐probe time delay varies. Microscopic many‐body calculations reveal that the experimental observations contain pronounced signatures of ponderomotive contributions, the ac‐Stark effect, and terahertz high harmonic generations. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Degree of entanglement of photon pairs generated from V‐type system in microcavity
Authors: Ajiki Hiroshi , Ishihara Hajime 
Published: October 2008

AbstractWe propose polarization‐entangled photon generation via resonant hyper‐parametric scattering of a V‐type system in microcavity. Although a bare V‐type system cannot generate entangled photon pairs, microcavity makes the generation possible because of the formation of dressed states.In the strong‐coupling limit, generation of non‐entangled co‐polarized photons is considerably suppressed due to the photon blockade effect. Furthermore, some entangled photons have different frequencies from those of the input fields, and thus, we can utilize spectral filtering in order to extract entangled photons. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of the time dependent photoluminescence of a J‐aggregate microcavity
Authors: Michetti Paolo , La Rocca Giuseppe C. 
Published: October 2008

AbstractWe have built a model for the optical dynamics of a strongly coupled J‐aggregate microcavity. Our model is based on the description of a J‐aggregate film as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. In a strongly coupled microcavity the excitation spectrum is modified due to the formation of the excitonpolaritons, in which the superradiant states of the optically resonant film are mixed with the cavity photons.The calculation of the steady‐state photoluminescence, following a constant non resonant pumping, explains the thermal activation of the upper polariton photoluminescence as a consequence of a bottleneck effect in the relaxation. The results of our calculation of the time dependent photoluminescence pumping following non resonant pulsed pumping are here presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface excitonic recombination dynamics in ZnO nanowires
Authors: Richters Jan‐Peter , Wischmeier Lars , Rückmann Ilja , Gutowski Jürgen , Voss Tobias 
Published: October 2008

AbstractThe optical properties of ZnO nanowires are strongly influenced by surface effects. For diameters smaller than 200 nm, a surface exciton recombination band is observed. We report on the recombination dynamics of this emission band using low temperature and time resolved photoluminescence spectroscopy. We find a biexponential decay with different decay constants for different emission wavelengths on the band. We present a model to explain the biexponential decay characteristics and report on possibilities to experimentally enhance the relative intensity of the surface exciton emission by embedding the ZnO nanowires into polymer matrices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ionization equilibrium and Mott transition in an excited semiconductor, phase diagram
Authors: Richter F. , Semkat D. , Kremp D. , Henneberger K. 
Published: October 2008

AbstractThe thermodynamic properties of an electron–hole plasma in a highly excited semiconductor are investigated. Special attention is directed to the influence of many‐particle effects like screening, lowering of the ionization energy, and Mott effect on the ionization equilibrium. In particular, the Mott effect limits the region of existence of excitons and, therefore, of a possible Bose–Einstein condensate at low temperatures. Results for the chemical potential and the degree of ionization are presented for cuprous oxide. A possible window for the occurrence of a BEC of excitons taking into account the Mott effect is shown. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature degradation of the gain transition in terahertz quantum cascade lasers – the role of acoustic phonon scattering
Authors: Nelander Rikard , Wacker Andreas 
Published: October 2008

AbstractThe temperature degradation in terahertz quantum cascade lasers is investigated with the focus on the role of acoustic phonon scattering. A self‐energy describing the electron‐acoustic phonon interaction is derived and used to study the importance in transport and optical properties.We observe a strong degradation of the gain peak with temperature. Despite the very small coupling to electrons, the exclusion of acoustic phonon scattering alters the current and peak gain in the order of 5%. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical study of phononassisted singlet‐singlet relaxation in two‐electron semiconductor quantum dot molecules
Authors: Grodecka Anna , Machnikowski Paweł , Förstner Jens 
Published: October 2008

AbstractPhonon‐assisted singlet‐singlet relaxation in semiconductor quantum dot molecules is studied theoretically. Laterally coupled quantum dot structures doped with two electrons are considered. We take into account interaction with acoustic phonon modes via deformation potential and piezoelectric coupling. We show that piezoelectric mechanism for the considered system is of great importance and for some ranges of quantum dot molecule parameters is the dominant contribution to relaxation.It is shown that the phonon‐assisted tunneling is much faster (down to ∼ 6 ps even at zero temperature) in comparison with other decoherence processes. The influence of Coulomb interaction is discussed and its consequences are indicated. We calculate the relaxation rates for GaAs quantum dot molecules and study the dependence on quantum dot size, distance and offset between the constituent quantum dots. In addition the temperature dependence of the tunneling rates is analyzed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Semiconductor excitons in strong terahertz fields
Authors: Steiner J. T. , Kira M. , Koch S. W. 
Published: October 2008

AbstractA microscopic theory for the nonlinear terahertz response of excited semiconductor systems is presented. It is shown that the measurable quantities in typical terahertz transmission/reflection experiments contain large ponderomotive contributions which mask the signatures from terahertz‐induced many‐body transitions. A scheme is developed to remove the ponderomotive contributions and applied to isolate the signatures of Rabi oscillations of an exciton population. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of strong lightmatter coupling in semiconductor quantum‐dot microcavities
Authors: Schneebeli L. , Kira M. , Koch S. W. 
Published: October 2008

AbstractMaxwell‐Bloch and luminescence equations are presented which describe vacuum Rabi splitting and the quantum rungs on the Jaynes‐Cummings ladder for strongly‐coupled dot‐cavity systems. Resonance fluorescence conditions are considered where an optical pump is exciting the dot‐cavity system while the re‐emitted light is detected.An analytical formula for the vacuum Rabi splitting is derived and a pumping mechanism for the direct generation of the second rung is presented and analyzed. An optimum pumping frequency and optimum pumping intensity are identified for the generation of the second rung. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exciton spin decay in quantum dots: single and double phonon ssisted transitions
Authors: Roszak K. , Machnikowski P. , Axt V. M. , Kuhn T. 
Published: October 2008

AbstractWe study phonon assisted transitions leading to exciton spin decay in quantum dots. We concentrate on couplings specific to the hole (Bir‐Pikus Hamiltonian) and the exciton as a whole (short‐range exchange interaction). A system strongly confined in a self‐assembled quantum dot is considered.We discuss single‐phonon assisted processes arising from the interplay of these interactions and show the dominating role of transverse phonons. We have also found a new two‐phonon assisted transition, connected with the interplay of different parts of the Bir‐Pikus Hamiltonian in the presence of the singlet‐triplet splitting. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamical model for coherent optical manipulation of a single spin state in a charged quantum dot
Authors: Slavcheva Gabriela 
Published: October 2008

AbstractThe optically‐induced coherent spin dynamics of a single spin confined in a charged quantum dot (QD) is theoretically studied employing coupled vector Maxwell‐pseudospin formalism. Generalized pseudospin master equation is derived for description of the time evolution of spin coherences and spin populations including spin population transfer and dissipation in the system through spin relaxation processes. The equation is solved in the time domain self‐consistently with the vector Maxwell equations for the optical wave propagation coupled to it via macroscopic medium polarisation. Using the model the long‐lived electron spin coherence left behind a single resonant ultrashort optical excitation of the electron‐trion transition in a charged QD is simulated in the low‐ and high‐intensity Rabi oscillations regime. Signatures of the polarised photoluminescence (PL), predicted by the model, such as the appearance of a second echo pulse after the excitation and characteristic PL trace shape, are discussed for realization of high‐fidelity schemes for coherent readout of a single spin polarisation state. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Four‐wave mixing optical response of an ensemble of quantum dot molecules
Authors: Sitek A. , Machnikowski P. 
Published: October 2008

AbstractFour‐wave mixing (FWM) optical response from a sample containing a non‐homogeneously broadened ensemble of vertically stacked pairs of quantum dots is studied theoretically. The effects of collective interaction between the dots and their electromagnetic environment are analyzed. It is shown that the shape of the FWM echo is affected by the coupling between the two dots and, to some extent, by the statistics of the ensemble.In the time‐integrated signal, oscillations on picosecond delay time scale appear which lead to a reduction of the coherent response for coupled dots. For longer delays, the evolution is dominated by radiative decay, with the decay rate increasing from Γ to 2Γ(superradiance effect) as the coupling becomes stronger. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Carrier‐carrier and carrier‐phonon scattering in the low‐density and low‐temperature regime for resonantly pumped semiconductor quantum dots
Authors: Seebeck J. , Lorke M. , Gartner P. , Jahnke F. 
Published: October 2008

AbstractWe study carrier relaxation due to Coulomb scattering and interaction with LO‐phonons in semiconductor quantum dots at low temperatures. Scattering for different relaxation process are evaluated for various carrier distributions that correspond to stages of the typical relaxation kinetics after optical excitation with a weak pulse, generating on average less than one electron per quantum dot.Even when the spacing of the quantum dot energy levels does not match the LO‐phonon energy, we.nd that carrier‐LO‐phonon scattering, in addition to electronelectron and electron‐hole interaction, provides efficient carrier relaxation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
THz measurements of the optical response in a two‐dimensional electron gas
Authors: Chatterjee S. , Grunwald T. , Köhler D. , Pierz K. , Golde D. , Kira M. , Koch S.W. 
Published: October 2008

AbstractWe present an experimental study of the THz transmission through a two dimensional electron gas embedded in a high electron‐mobility transistor‐like structure. Similar to previous experiments in a three‐dimensional system, a clear resonance is observed in the imaginary part of the inverse dielectric function ℱ{1/ε (ω)}. A detailed analysis using a Drude‐like response cannot explain all experimental findings. These significant deviations make a more detailed microscopic analysis necessary. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular dynamics simulation on HP1 protein binding by histone H3 tail methylation and phosphorylation
Authors: Jiang Yan‐Ke , Zou Jian‐Wei , Wu Yu‐Qian , Zhang Na , Yu Qing‐Sen , Jiang Yong‐Jun 
Published: October 2008

AbstractTrimethylation of histone H3 lysine 9 is important for recruiting heterochromatin protein 1 (HP1) to discrete regions of the genome, thereby regulating gene expression, chromatin packaging, and heterochromatin formation. Phosphorylation of histone H3 has been linked with mitotic chromatin condensation. During mitosis in vivo, H3 lysine 9 methylation and serine 10 phosphorylation can occur concomitantly on the same histone tail, whereas the influence of phosphorylation to trimethylation H3 tail recruiting HP1 remains controversial. In this work, molecular dynamics simulation of HP1 complexed with both trimethylated and phosphorylated H3 tail were performed and compared with the results from the previous methylated H3‐HP1 trajectory. It is clear from the 10‐ns dynamics simulation that two adjacent posttranslational modifications directly increase the flexibility of the H3 tail and weaken HP1 binding to chromatin. A combinatorial readout of two adjacent posttranslational modifications—a stable methylation and a dynamic phosphorylation mark—establish a regulatory mechanism of protein–protein interactions. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Ab‐initio studies of magnetic properties of small‐sized and cuboctahedral aluminum nanoclusters
Authors: Phung T. V. B. , Hashimoto T. , Nishikawa K. , Nagao H. 
Published: October 2008

AbstractMagnetic properties of Aln clusters are investigated using ab initio density functional calculations based on plane‐wave and the all electron projector augmented‐wave (PAW) method. We present stable structures of small‐sized Aln (n = 2–17) clusters obtained from optimization with binding energy, magnetization, and compared our results with experiment data. The size dependence of binding energy and magnetization are clarified. For large clusters, we discuss the stability of cuboctahedral Aln clusters with up to 923 atoms based on the size dependent binding energy. The coefficients corresponding to surface and edge energies for cuboctahedral Aln clusters have been estimated. We have obtained the cohesive energy of the bulk system to be Ec = 3.418 eV, close to the experimental value (3.39 eV) through the fitting function of size dependent binding energy. We discuss the magnetization of cuboctahedral Aln clusters in relation to shell structure. When the size of the cluster is enlarged, the distribution of magnetization shows that the spin density is largest at the outmost shell. From Al309 to Al923 clusters, electron and spin density in the center and innermost shell behave similar to the bulk. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Identification of lysophosphatidylcholine (LPC) and platelet activating factor (PAF) from PC12 cells and mouse cortex using liquid chromatography/multi‐stage mass spectrometry (LC/MS3)
Authors: Smith Jeffrey C. , Hou Weimin , Whitehead Shawn N. , Ethier Martin , Bennett Steffany A. L. , Figeys Daniel 
Published: October 2008

AbstractLipids play essential roles in cellular structural support, energy storage and signal transduction. Recently, mass spectrometry (MS) has been used to produce three‐dimensional maps that elucidate the lipid composition of complex cellular lysates. The identification of individual lipids within these maps is slow and requires the synthesis and spiking of each candidate lipid. We present a novel MS‐based technique that rapidly elucidates the atomic connectivity of the fatty acid/alcohol substituent on the sn‐1 position of several different families of glycerophosphocholine‐containing lipids within the confines of a chromatographic separation. Sodiated lipid species were fragmented to produce radical cations which lost successive methylene groups upon further collisional activation to reveal the identity of the parent molecule. This approach was demonstrated to be effective on isobaric members of the lysophosphatidylcholine (LPC) and platelet activating factor (PAF) families of glycerophospholipids. We demonstrate the application of this technique to unambiguously identify these species within complex cellular lysates and tissue extracts. Copyright © 2008 John Wiley & Sons, Ltd.
Structure and stability of B5C and C5B clusters
Authors: Liu Chunhui , Liu Lili , Han Peilin , Tang Mingsheng , Fu Huafeng 
Published: October 2008

AbstractGeometry optimizations and vibrational frequencies of B5C and C5B clusters were calculated with the Becke‐3LYP method using the 6‐311+G(d) basis set and some stable configurations of B5C and C5B clusters have been found. The most stable structure of B5C is a planar six‐membered ring. However, for C5B clusters, the most stable structure is linear with a boron atom in position 3. Various configurations of B5C clusters containing three‐membered boron rings have predominance in energy, whereas various configurations of C5B clusters containing three‐membered carbon rings are disadvantageous in energy. In B5C clusters, isomer2 can be converted into isomer1 by surmounting an energy barrier of 43.83 kJ.mol−1. In C5B clusters, the conversions of isomer5 into isomer2 and isomer7 into isomer2 have energy barriers of 19.66 and 20.57 kJ.mol−1, respectively. Copyright © 2008 John Wiley & Sons, Ltd.