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1.
Lippitz M Hübner CG Christ T Eichner H Bordat P Herrmann A Müllen K Basché T 《Physical review letters》2004,92(10):103001
We have investigated electronic excitation transfer in individual molecular dimers by time and spectrally resolved confocal fluorescence microscopy. The single molecule measurements allow for directly probing the distribution of the electronic coupling strengths due to static disorder in the polymer host. We find dimers where the excitation is delocalized (superradiant emission) while for others emission originates from a localized state. Transitions between delocalized and localized states as observed for a given dimer are attributed to structural fluctuations of the guest-host system. 相似文献
2.
The magnetic circular dichroism of III-V diluted magnetic semiconductors, calculated within a theoretical framework suitable for highly disordered materials, is shown to be dominated by optical transitions between the bulk bands and an impurity band formed from magnetic dopant states. The real-space Green's functions incorporate spatial correlations in the disordered conduction band and valence-band electronic structure, and include extended and localized states on an equal basis. Our findings reconcile unusual trends in the experimental magnetic circular dichroism in III-V diluted magnetic semiconductors with the antiferromagnetic p-d exchange interaction between a magnetic dopant spin and its host. 相似文献
3.
Femtosecond dynamics of excess electrons photo-injected into amorphous and crystalline D2O layers on Ru(0 0 1) have been investigated by time-resolved two-photon photoelectron spectroscopy. In the crystalline case, excited electrons are transferred into delocalized states considered as image potential states in the conduction band of ice and relax back to the metal on an ultrafast time scale. The life time of the n = 1 image potential state is <5 fs. In the amorphous case, spectral features arise from delocalized and localized electronic states. Relaxation of delocalized electrons back to the metal is as fast as in the crystalline case. The binding energy of localized electrons, however, is found to increase as a function of time delay by 1 eV/ps, which is attributed to the formation of solvated electrons. Such energetic stabilization starting at the bottom of the conduction band is clearly absent in crystalline layers. This pronounced correlation of electronic structure and electron dynamics with molecular structure is associated with the presence of localized states near the bottom of the conduction band in amorphous ice. Such localized states are absent for perfect periodic crystalline structures but prevail in amorphous systems where they serve as precursor sites for electron solvation. 相似文献
4.
We study numerically the ground state magnetization for clusters of interacting electrons in two dimensions in the regime where the single particle wave functions are localized by disorder. It is found that the Coulomb interaction leads to a spontaneous ground state magnetization. For a constant electronic density, the total spin increases linearly with the number of particles, suggesting a ferromagnetic ground state in the thermodynamic limit. The magnetization is suppressed when the single particle states become delocalized. 相似文献
5.
在密度泛函理论框架下的局域密度近似方法 (LDA)能够准确地给出广延态电子体系的基态电子结构 ,是研究复杂体系的电子结构的一种非常成功的方法。由于这种方法不含参数 ,被广泛地用于微观体系的研究。但是 ,在处理的体系中含有局域电子时 ,由于方法的局限 ,给出的结果与光电子谱等试验结果符合得并不好。LSDA U方法是在局域自旋密度近似的框架下 ,结合模型哈密顿方法 ,对局域电子采用哈伯德模型描述 ,用以改进局域密度近似计算的一种方法。本文利用局域密度近似下的离散变分团簇方法 (DVM )对于内嵌稀土原子的富勒烯Er2 @C82 、Tm @C82 的电子结构进行了第一性原理的计算。对于体系中所含的稀土原子存在强关联的 4f电子 ,在LDA方法计算的基础上 ,考虑 4f电子在位库仑作用 ,用LSDA U方法研究了上述体系 ,得到了可以和XPS和吸收谱相比较的结果。 相似文献
6.
7.
A. O. Govorov K. Karrai R. J. Warburton A. V. Kalameitsev 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):295
We describe theoretically multiply-charged excitons interacting with a continuum of delocalized states. Such excitons exist in relatively shallow quantum dots and have been observed in recent optical experiments on InAs self-assembled dots. The interaction of an exciton and delocalized states occurs via Auger-like processes. To describe the optical spectra, we employ the Anderson-like Hamiltonian by including the interaction between the localized exciton and delocalized states of the wetting layer. In the absence of a magnetic field, the photoluminescence line shapes exhibit interference effects. When a magnetic field is applied, the photoluminescence spectrum demonstrates anticrossings with the Landau levels of the extended states. We show that the magnetic-field behavior of charged excitons is very different to that of diamagnetic excitons in three and two-dimensional systems. 相似文献
8.
C.D. Pinheiro E. Longo E.R. Leite F.M. Pontes R. Magnani J.A. Varela P.S. Pizanni T.M. Boschi F. Lanciotti 《Applied Physics A: Materials Science & Processing》2003,77(1):81-85
We discuss the nature of visible photoluminescence at room temperature in amorphous strontium titanate in the light of the
results of a recent experimental and quantum mechanical theoretical study. Our calculation of the electronic structure involves
the use of first-principles molecular calculations to simulate the variation of the electronic structure in the strontium
titanate crystalline phase, which is known to have a direct band gap, and we also make an in-depth examination of amorphous
strontium titanate. The results of our simulations of amorphous strontium titanate indicate that the formation of five-fold
coordination in the amorphous system may introduce delocalized electronic levels in the highest occupied molecular orbital
and the lowest unoccupied molecular orbital. These delocalized electronic levels are ascribed to the formation of a tail in
the absorbance-spectrum curve. Optical absorption measurements experimentally showed the presence of a tail. The results are
interpreted by the nature of these exponential optical edges and tails associated with defects promoted by the disordered
structure of the amorphous material. We associate them with localized states in the band gap.
Received: 15 January 2002 / Accepted: 7 August 2002 / Published online: 4 December 2002
RID="*"
ID="*"Corresponding author. Fax: +55-16/2615-215, E-mail: derl@power.ufscar.br 相似文献
9.
Dorchies F Lévy A Goyon C Combis P Descamps D Fourment C Harmand M Hulin S Leguay PM Petit S Peyrusse O Santos JJ 《Physical review letters》2011,107(24):245006
X-ray absorption near-edge spectroscopy (XANES) is a powerful probe of electronic and atomic structures in various media, ranging from molecules to condensed matter. We show how ultrafast time resolution opens new possibilities to investigate highly nonequilibrium states of matter including phase transitions. Based on a tabletop laser-plasma ultrafast x-ray source, we have performed a time-resolved (~3 ps) XANES experiment that reveals the evolution of an aluminum foil at the atomic level, when undergoing ultrafast laser heating and ablation. X-ray absorption spectra highlight an ultrafast transition from the crystalline solid to the disordered liquid followed by a progressive transition of the delocalized valence electronic structure (metal) down to localized atomic orbitals (nonmetal-vapor), as the average distance between atoms increases. 相似文献
10.
K-edge XANES spectra of sulfur in ErS and PrS have been measured. A detailed analysis of the electronic structure of ErS and PrS was carried out by the full-scale multiple scattering method, and a good agreement with experimental spectra was obtained. The fine structure of unoccupied sulfur states in the conduction band was determined. The unoccupied d states of praseodymium in PrS are shown to interact with the sulfur p states to expel the sulfur delocalized states from the energy region where the states of the rare-earth elements are localized. 相似文献
11.
We study the properties of the spinor wavefunction in a strongly disordered environment on a two-dimensional lattice. By employing a transfer-matrix calculation we find that there is a transition from delocalized to localized states at a critical value of the disorder strength. We prove that there exists an Anderson localized phase with exponentially decaying correlations for sufficiently strong scattering. Our results indicate that suppressed backscattering is not sufficient to prevent Anderson localization of surface states in topological insulators. 相似文献
12.
Quantum operations with a charge solid-state qubit whose logical states are formed by two spatially separated localized states of an electron in the double-dot structure are studied theoretically. We show that it is possible to perform various one-qubit rotations making use of the microwave pulses tuned to the resonances between the localized states and the excited state delocalized over the nanostructure. An explicit analytic expression for the time-dependent electron state vector is derived, and the appropriate pulse parameters are determined. 相似文献
13.
J. Lages D. L. Shepelyansky 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(2):237-244
We propose a physical picture of superinsulator observed recently in experiments with superconducting films
in a magnetic field. On the basis of previous numerical studies we argue that a moderate attraction creates bi-particle localized
states at intermediate disorder strength when noninteracting electron states are delocalized and metallic. Our present numerical
study
show that such localized pairs are broken by a static electric field which strength is above a certain threshold.
We argue that such a breaking of localized pairs by a static field is at the origin of superinsulator breaking
with a current jump observed experimentally above a certain critical voltage. 相似文献
14.
We report the observation of enhanced near-infrared transmission through arrays of subwavelength coaxial metallic structures compared with that through comparable diameter hole arrays as a result of localized electromagnetic modes supported by the complex coaxial unit cell. Polarization and angle-dependent transmission measurements clearly demonstrate the coupling between this localized mode and delocalized surface plasmon modes. A generalized, multiple discrete states Fano line shape provides a good fit to the experimental results. 相似文献
15.
A. Sukhanovsky V. Batalov A. Teymurazov P. Frick 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):9
Considering the nonlinearity arising from the interaction between electrons and lattice
vibrations, an effective electronic model with a self-interaction cubic term is employed
to study the interplay between electron-electron and electron-phonon interactions. Based
on numerical solutions of the time-dependent nonlinear Schroedinger equation for an
initially localized two-electron singlet state, we show that the magnitude of the
electron-phonon coupling χ necessary to promote the self-trapping of the
electronic wave packet decreases as a function of the electron-electron interaction
U. We show that such dependence is directly linked to the narrowing of
the band of bounded two-electron states as U increases. We obtain the
transition line in the χ × U parameter space separating
the phases of self-trapped and delocalized electronic wave packets. The present results
indicates that nonlinear contributions plays a relevant role in the electronic wave packet
dynamics, particularly in the regime of strongly correlated electrons. 相似文献
16.
The interplay of isotropic exchange, antisymmetric (AS) exchange, and electron delocalization has been theoretically investigated for a system comprising two triangles, one with three localized d1 spins, which gives rise to spin frustration effects, and the other with one d1 center delocalized on the three sites. In the localized limit the AS exchange is partially reduced by the low symmetry components of an isotropic exchange (inter-triangle interaction) and splits the spin triplets only in the second order, contrary to what is found for a single triangular system where splitting of the spin doublet levels occurs in the first order. Zero-field splitting parameters depend on both AS exchange parameters and low symmetry components of the isotropic exchange. The EPR spectrum consists of intratriplet (Heisenberg type) and intertriplet (non-Heisenberg type) lines. AS exchange also induces singlet-triplet transitions. The EPR spectra of powder samples are generated for a domain of key parameters. Two different situations occur depending on the symmetry of the electronic states when the electron delocalization is taken into account. The orbital doublets of the localized system indicate a complete averaging of the exchange interactions, which results in effective enhancement of AS exchange. Unlike triplets, the orbital singlets are unaffected by a transfer process, developing only second-order AS exchange. Coexistence of localized and delocalized states is expected to be an intrinsic feature of exchange systems with partial delocalization. The relevance of these effects to the magnetic properties of exchange clusters is briefly discussed. 相似文献
17.
W. S. Dias M. L. Lyra F. A. B. F. de Moura 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):7
Considering the nonlinearity arising from the interaction between electrons and latticevibrations, an effective electronic model with a self-interaction cubic term is employedto study the interplay between electron-electron and electron-phonon interactions. Basedon numerical solutions of the time-dependent nonlinear Schroedinger equation for aninitially localized two-electron singlet state, we show that the magnitude of theelectron-phonon coupling χ necessary to promote the self-trapping of theelectronic wave packet decreases as a function of the electron-electron interactionU. We show that such dependence is directly linked to the narrowing ofthe band of bounded two-electron states as U increases. We obtain thetransition line in the χ × U parameter space separatingthe phases of self-trapped and delocalized electronic wave packets. The present resultsindicates that nonlinear contributions plays a relevant role in the electronic wave packetdynamics, particularly in the regime of strongly correlated electrons. 相似文献
18.
Kim BJ Jin H Moon SJ Kim JY Park BG Leem CS Yu J Noh TW Kim C Oh SJ Park JH Durairaj V Cao G Rotenberg E 《Physical review letters》2008,101(7):076402
We investigated the electronic structure of 5d transition-metal oxide Sr2IrO4 using angle-resolved photoemission, optical conductivity, x-ray absorption measurements, and first-principles band calculations. The system was found to be well described by novel effective total angular momentum Jeff states, in which the relativistic spin-orbit coupling is fully taken into account under a large crystal field. Despite delocalized Ir 5d states, the Jeff states form such narrow bands that even a small correlation energy leads to the Jeff=1/2 Mott ground state with unique electronic and magnetic behaviors, suggesting a new class of Jeff quantum spin driven correlated-electron phenomena. 相似文献
19.
From the theory of many-electron states in atoms, we know that there exists a strong Coulomb repulsion, which results in the
electronic term structure of atoms and is responsible for Hund’s rules. By expanding the Coulomb on-site repulsion into a
multipolar series, we derive this interaction and show that it is also present in solids as a correlation effect, which means
that the interaction requires a multideterminant version of the Hartree-Fock method. Of particular interest is the case where
this interaction couples states of localized (f) and delocalized (s) electrons. We show that the interaction is bilinear in the creation/annihilation operators for localized electrons and bilinear
in the operators for conduction electrons. To study the coupling, we consider a simple model in the framework of an effective
limited configuration interaction method with one localized f-electron and one itinerant s-electron per crystal site. The on-site multipole interaction between the f- and s-electrons is explicitly taken into account. It is shown that depending on the low-lying excitation spectrum imposed by the
crystal electric field, the model can lead not only to ferromagnetism but also to a nonmagnetic state. The model is relevant
for solids with localized and itinerant electron states. 相似文献
20.
L. Petit A. Svane W.M. Temmerman Z. Szotek 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):139-146
The electronic and magnetic properties of Pu monopnictides and monochalcogenides, PuX (X = N, P, As, Sb, Bi, O, S, Se, Te, Po), are studied using the self-interaction-corrected local spin-density approximation. This approach allows for an integer number of f-states to be localized, while the remaining f-electron degrees of freedom are available for band formation. By varying the relative proportions of localized and delocalized
f-states, the energetically most favourable (groundstate) configuration can be established. We show that the experimental data
can be interpreted in terms of the coexistence of both localized and delocalized f-states.
Received 10 August 2001 相似文献