Electronic Excitations In Solids Research Articles

Channel-closing effects of electronic excitation in solids.

We investigate the electronic excitation of solids in strong fields by solving the time-dependent Schrödinger equation. The excitation probability exhibits a strong modulation as a function of laser intensity when the initial states fill in the whole valence band. To have a clear insight into the modulation, we further study the electronic excitation from a single eigenstate in solids. A series of resonance-like enhancements of excitation probability are produced by changing the laser intensity and wavelength. We attribute the resonance-like enhancements to the channel-closing effects in solids. It is shown that the excitation probability exhibits enhancements when the value of channel is odd for intracycle interference and an integer for intercycle interference. This is different from the atom that the enhancement occur in the integer channels. We also reveal that the channel-closing effects can be observed by solid high-order harmonic generation.

A high-energy-resolution resonant inelastic X-ray scattering spectrometer at ID20 of the European Synchrotron Radiation Facility.

An end-station for resonant inelastic X-ray scattering and (resonant) X-ray emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high-energy-resolution applications, including partial fluorescence yield or high-energy-resolution fluorescence detected X-ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non-resonant inelastic X-ray scattering measurements of valence electron excitations.

Effect of Point Defects on Optical Properties of Graphene Fluoride: A First-Principles Study

The experimental optical gap of graphene fluoride has been measured between 3.1 and 3.8 eV, which is much smaller than the corresponding theoretical predictions (∼5.1–5.7 eV). To resolve this discrepancy, we examine the optical properties of graphene fluoride in the presence of point defects. We employ a first-principles method for large-scale calculations of electronic excitations in solids based on density functional theory with optimally tuned and range-separated hybrid (OT-RSH) functionals. The method is validated for lithium fluoride, graphene fluoride, and phosphorene with excellent agreement to previous computational and experimental results. We reveal that the optoelectronic properties of graphene fluoride can be influenced profoundly by a small amount of fluorine vacancies and exciton binding energy in graphene fluoride can be doubled by a small concentration of oxygen substitutional defects. These point defects are believed to be responsible for the discrepancy in the optical gaps between the th...

Angular self-localization of impurities rotating in a bosonic bath

The existence of a self-localization transition in the polaron problem has been under an active debate ever since Landau suggested it 83 years ago. Here we reveal the self-localization transition for the rotational analogue of the polaron -- the angulon quasiparticle. We show that, unlike for the polarons, self-localization of angulons occurs at finite impurity-bath coupling already at the mean-field level. The transition is accompanied by the spherical-symmetry breaking of the angulon ground state and a discontinuity in the first derivative of the ground-state energy. Moreover, the type of the symmetry breaking is dictated by the symmetry of the microscopic impurity-bath interaction, which leads to a number of distinct self-localized states. The predicted effects can potentially be addressed in experiments on cold molecules trapped in superfluid helium droplets and ultracold quantum gases, as well as on electronic excitations in solids and Bose-Einstein condensates.

Superradiant Emission from a Collective Excitation in a Semiconductor.

We report an anomalous wide broadening of the emission spectra of an electronic excitation confined in a two-dimensional potential. We attribute these results to an extremely fast radiative decay rate associated with superradiant emission from the ensemble of confined electrons. Lifetimes extracted from the spectra are below 100 fs and, thus, 6 orders of magnitude faster than for single particle transitions at similar wavelength. Moreover, the spontaneous emission rate increases with the electronic density, as expected for superradiant emission. The data, all taken at 300 K, are in excellent agreement with our theoretical model, which takes into account dipole-dipole Coulomb interaction between electronic excitations. Our experimental results demonstrate that the interaction with infrared light, which is usually considered a weak perturbation, can be a very efficient relaxation mechanism for collective electronic excitations in solids.

ChemInform Abstract: Electronic Excitations in Light Absorbers for Photoelectrochemical Energy Conversion: First Principles Calculations Based on Many Body Perturbation Theory

AbstractReview: 261 refs.

Electronic excitations in light absorbers for photoelectrochemical energy conversion: first principles calculations based on many body perturbation theory

We describe state of the art methods for the calculation of electronic excitations in solids and molecules, based on many body perturbation theory, and we discuss some applications of these methods to the study of band edges and absorption processes in representative materials used as photoelectrodes for water splitting.

First-Principles Calculation of Electronic Excitations in Solids with SPEX

Abstract We describe the software package SPEX, which allows first-principles calculations of quasiparticle and collective electronic excitations in solids using techniques from many-body perturbation theory. The implementation is based on the full-potential linearized augmented-plane-wave (FLAPW) method, which treats core and valence electrons on an equal footing and can be applied to a wide range of materials, including transition metals and rare earths. After a discussion of essential features that contribute to the high numerical efficiency of the code, we present illustrative results for quasiparticle band structures calculated within the GW approximation for the electronic self-energy, electron-energy-loss spectra with inter- and intraband transitions as well as local-field effects, and spin-wave spectra of itinerant ferromagnets. In all cases the inclusion of many-body correlation terms leads to very good quantitative agreement with experimental spectroscopies.

Electronic excitations in solids: Density functional and Green's function theory

AbstractTheoretical approaches for ab initio studies of the electronic and optical properties of matter are here reviewed. Examples within Density Functional Theory, Many‐Body perturbation Theory and Time Dependent Density Functional Theory are presented and discussed, pointing out advantages and drawbacks of the different schemes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pressure-induced electron transfer in cobalt-iron Prussian blue complex studied by RIXS

Resonant Inelastic X-ray Scattering (RIXS) recently has become one of the most advanced techniques that probe electronic excitations in solids, combining both advantages of a high resolution and bulk sensitivity. In our measurement, we attempted to study the charge transfer in K0.2Co1.4[Fe(CN)6]•XH2O as a function of pressure by RIXS. The photoinduced magnetization at low temperature in Co-Fe Prussian blue analogues was explained by the presence of diamagnetic Co(III)-Fe(II) low spin pairs, this step can be pushed by low temperature or high pressure. Then the photoinduced electron transfer from Fe(II) to Co(III) can be happened. We had performed a preliminary Resonant inelastic x-ray scattering (RIXS) studies on the K0.2Co1.4[Fe(CN)6]•XH2O at 0.33GPa under Diamond Anvil Cell(DAC) to study and confirmed the charge transfer behavior successfully during this time. From the comparison of the title compound at 0.33GPa pressure and ambient pressure, we can see the Co(III) ratio increase very clearly, that mean the charge transfer Fe(III)-Co(II)→Fe(II)-Co(III) happened. This confirms the outstanding resolving power of RIXS and fruitful quantitative determinate the ligand field strength and also the Co(II)/[Co(II)+Co(III)] ratio can be determinated from this kind of measurement. In here, we will present the measurement results on Iron K-edge and Cobalt K-edge partial fluorescence yield mode (PFY) by RIXS experiment to get the ligand field strength and charge transfer information related with pressure.

Nucleation of nanoclusters in thermal spikes in solids irradiated with swift heavy ions

It was observed recently that decay of supersaturated solid solution of impurity atoms in materials irradiated with swift heavy ions results in nanocluster formation correlating with the value of the electronic energy loss of projectiles. Manifesting new possibilities for governing the nanosize structure transformation, this effect is interesting for the fundamental problem of phase separations caused by energetic electronic excitations in solids as well as for modern nanotechnologies. In this paper the effect of the `thermal spike', when the energy transfer from the excited electrons to target atoms results in the material heating in the track, on the nucleation of nanoclusters is investigated. It is assumed that the precipitation can occur if the temperature in the track reaches such value that the nucleation time becomes shorter than the track cooling time.

Electronic excitations investigated by inelastic x-ray scatteringspectroscopy

It is shown how non-resonant and resonant inelastic x-ray scatteringspectroscopy (IXSS) offer valuable information about electronic excitations insolids. After a presentation of the basic relations, applications of IXSS on alarge variety of systems and electronic excitations are discussed, where inmost cases synchrotron radiation is utilized

Electronic excitations in solids during impact of atomic particles

One- and two-electron non-adiabatic models of ion formation in sputtering are briefly reviewed and compared with experiments on ion emission from Cu and from GaAs. Using these examples it is shown that in order to explain the experiments the models must be extended and must include substrate excitations described tentatively by an electronic temperature. Such approach allows for a consistent elucidation of the experimental data. Possible consequences of many-electron excitation processes for electron emission from bombarded solids are also considered.

Bond scission induced by electronic excitation in solids: A tool for nanomanipulation

A review is given on the atomic processes induced by electronic excitation of nonmetallic solids, including defect formation, transformation of defect structures, atomic emission from surfaces and surface modifications. It is pointed out that the processes involve bond scission. Two major issues, the localization of the electronic excitation energy and the energetics, are discussed. It is emphasized that the major features of the processes are different, depending on the presence and absence of self-trapping of excitons and on the bond strength with respect to the band-gap energy. Bond scission can be induced at any sites in solids in which excitons are self-trapped, but only at defect sites in solids in which excitons are not self-trapped. The yield of the bond scission is a superlinear function of the density of excitation when the bond energy is higher than the band-gap energy. For semiconductor surfaces, on which excitons are not self-trapped and the bond strength is higher than the band-gap energy, bond scission is induced only at the sites of surface defects and its yield is a superlinear function of the density of excitation.

Flux and resolution requirements for studies of electronic excitations in solids (invited)

Advances in synchrotron sources promise to open a new frontier in the use of inelastic x-ray scattering to probe electronic excitations on the eV and sub-eV energy scales. In this paper we present the flux and resolution requirements for inelastic scattering in condensed matter systems. A review of several recent results will be given along with several proposed experiments.

Alternative Methods for Sub-eV Resolution Inelastic X-ray Scattering (invited)

A synopsis of SRI workshop 9 held on October 20, 1995, is given. Details concerning the oral presentations of speakers not contributing to these proceedings are included. The workshop consisted of the following invited presentations: 1. M. Schwoerer-Boehning (APS), ‘‘Experimental Needs for Milli-eV Resolution Inelastic X-ray Scattering, ’’ 2. E. E. Alp (APS), ‘‘Inelastic Nuclear Resonant X-ray Scattering,’’ 3. A. Baron (ESRF), ‘‘ Inelastic X-ray Scattering via Nuclear Resonant Analyzer,’’ 4. D. E. Moncton (APS), ‘‘ An Exact Backscattering Beamline,’’ 5. A. Caticha (SUNY-Albany), ‘‘X-ray Fabry-Perot Cavities,’’ 6. E. D. Isaacs (AT&T Bell Labs), ‘‘Flux and Resolution Requirements for Studies of Electronic Excitations in Solids,’’ 7. C. K. Stahle (NASA), ‘‘Hard X-ray Detectors with Very High Energy Resolution,’’ 8. A. K. Freund (ESRF), ‘‘Mosaic Crystal Analyzers.’’ These proceedings contain separate papers by Caticha, Isaacs, and Stahle for the above listed presentations, and we will not discuss them further here. The other presentations are summarized below.

Laser-Beam Interaction with Defects on Semiconductor Surfaces: An Approach to Generation of Defect-Free Surfaces

Current studies of laser-ind uced emissions of semiconductor atoms from semiconductor surf ace s, originating from electronic bond breaking, are reviewed. Electronic excitation in solids can lead to atomic emissions by breaking the bonds of the surf ace atoms. For semiconductor surfac es, this process requires multiple excitations and is defect related. Experimental results of atomic emissions induced by nanosecond laser pulses on Si, GaAs, and GaP surfaces show that the emission originates from surface

Fermi surface instabilities and unusual spectral properties in low-dimensional systems

Photoelectron spectroscopy can probe low energy electronic excitations in solids, with practical limitations set by the experimental energy and angular resolution. Appropriate conditions can now be achieved which allow us to visualize changes in the electronic states near the Fermi surface at phase transitions, namely in two-dimensional materials. Quasi one-dimensional conductors are unique in their apparent failure to exhibit a clear metallic signature. This unusual spectroscopic behavior might be the consequence of the singular nature of electronic correlations in 1D.

Large Scale Atomic Migration Induced by Electronic Excitation in Solids

Large Scale Atomic Migration Induced by Electronic Excitation in Solids

Formation of localized states and electronic excitation in solids during low-energy particle bombardment

The excitation of deep holes (2s, 2p, in Al) in collision cascades is known to be responsible for emission of high-energy secondary electrons from solids bombarded by fast particles. The excitation occurs above certain impact energy threshold ( ≈ 800 eV in the case of Al) which is given by the minimum interatomic distance in the binary atomic collision needed for inner shell-valence band energy crossing ( ≈ 0.5 Å in Al). Experiments indicate however, that electrons may be emitted from solids far below the deep-hole excitation threshold. The classical valence electron-particle binary collision mechanism which is responsible for most of the particle electronic energy losses yields only low energy electrons which cannot overcome the work function of solids. We have found out that in collision cascades the deformation of valence electron clouds in more complex collision can lead to localized levels below the bottom of the conduction band of a metal. When these levels loose electrons during dynamical particle-particle interactions their subsequent filling by Auger processes could lead to electron emission. Using a cluster of 123 Al atoms with 3s and 3p overlapping Gaussian orbitals and using the pseudopotential of solid Al we have calculated the localization and energies of these new time-dependent electronic states for some collision configurations. We have also estimated the probability of the hole occupation of such states induced by the dynamics of particle cascades.