Absolute Band Mapping by Combined Angle-Dependent Very-Low-Energy Electron Diffraction and Photoemission: Application to Cu

Strocov, Vladimir N.; Claessen, R.; Nicolay, G.; Hüfner, S.; Kimura, Akio; Harasawa, Ayumi; Shin, Shik; Kakizaki, Akito; Nilsson, P. O.; Starnberg, H. I.; Blaha, Peter

doi:10.1103/physrevlett.81.4943

Cited by 71 publications

(86 citation statements)

References 46 publications

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“…27 A typical bottleneck is given by the summations over the empty states , both for the determination of the screening and for G. Another difficulty comes from the convergence of Brillouin zone integrals (i.e., k-point sampling) of functions that have a factor ͉kϩG͉ 2 in the denominator as the exchange term (Pulci, 1998 (Marini et al, 2002); dashed line, DFT-LDA eigenvalues; ᭺, experimental data compiled by Courths and Hü fner (1984). A comparison to more recent experimental data (Strocov et al, 1998(Strocov et al, , 2001) yields the same agreement.…”

Section: A Evaluation Of the Green's Function Gsupporting

confidence: 73%

Electronic excitations: density-functional versus many-body Green’s-function approaches

2002

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Electronic excitations lie at the origin of most of the commonly measured spectra. However, the first-principles computation of excited states requires a larger effort than ground-state calculations, which can be very efficiently carried out within density-functional theory. On the other hand, two theoretical and computational tools have come to prominence for the description of electronic excitations. One of them, many-body perturbation theory, is based on a set of Green's-function equations, starting with a one-electron propagator and considering the electron-hole Green's function for the response. Key ingredients are the electron's self-energy ⌺ and the electron-hole interaction. A good approximation for ⌺ is obtained with Hedin's GW approach, using density-functional theory as a zero-order solution. First-principles GW calculations for real systems have been successfully carried out since the 1980s. Similarly, the electron-hole interaction is well described by the Bethe-Salpeter equation, via a functional derivative of ⌺. An alternative approach to calculating electronic excitations is the time-dependent density-functional theory (TDDFT), which offers the important practical advantage of a dependence on density rather than on multivariable Green's functions. This approach leads to a screening equation similar to the Bethe-Salpeter one, but with a two-point, rather than a four-point, interaction kernel. At present, the simple adiabatic local-density approximation has given promising results for finite systems, but has significant deficiencies in the description of absorption spectra in solids, leading to wrong excitation energies, the absence of bound excitonic states, and appreciable distortions of the spectral line shapes. The search for improved TDDFT potentials and kernels is hence a subject of increasing interest. It can be addressed within the framework of many-body perturbation theory: in fact, both the Green's functions and the TDDFT approaches profit from mutual insight. This review compares the theoretical and practical aspects of the two approaches and their specific numerical implementations, and presents an overview of accomplishments and work in progress. CONTENTS

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Section: A Evaluation Of the Green's Function Gsupporting

confidence: 73%

Electronic excitations: density-functional versus many-body Green’s-function approaches

2002

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“…Our comparison of the experimental quasiparticle and DFT energies thus directly yields ∆Σ. The ∆Σ values in the X-point, corresponding in our experiment 7 to K = 0, are given in Table 1 compared to the GW calculations.…”

Section: Self-energy Correctionsmentioning

confidence: 96%

“…Only recently, based on comparison of new angle-resolved photoemission (PE) data obtained under full control of the 3-dimensional wavevector k with state-of-art DFT calculations, we have demonstrated that the self-energy corrections ∆Σ = E(k) − ε(k) to the DFT in the valence band of Cu display a clear k-and band dependence, reaching values as large as 0.5 eV in the d-bands. 7 These results gave a serious indication for the importance of self-energy effects even in such a supposedly simple metal as Cu. In fact, the previous misconception had arisen only due to errors of the early DFT calculations which accidentally matched ∆Σ.…”

Section: Introductionmentioning

confidence: 99%

“…They are perfectly consistent with the whole body of previous experimental data compiled in [6], but have a superior accuracy by virtue of employing a combined VLEED-PE method in which VLEED was used to achieve full control of the 3-dimensional k. The experimental E(k) is shown in Fig.2 also compared with the calculations. The original data from [7] was processed to include only the peaks relevant to the bulk states and compensate the lifetime induced intrinsic shifts of the PE peaks notable in the bottom of the sp-band (∼ 0.1eV ). In principle, the accuracy of these data can be further improved by correcting for possible intrinsic shifts due to the surface and matrix element effects, but this would require demanding calculations within the one-step PE theory.…”

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confidence: 99%

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Band- andk-dependent self-energy effects in the unoccupied and occupied quasiparticle band structure of Cu

et al. 2002

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Excited-state self-energy effects in the electronic structure of Cu, a prototype weakly correlated system containing states with different degrees of localization, are investigated with emphasis on the unoccupied states up to 40 eV above the Fermi level. The analysis employs the experimental quasiparticle states mapped under full control of the 3-dimensional wavevector k using very-low energy electron diffraction for the unoccupied states and photoemission for the occupied states. The self-energy corrections to the density-functional theory show a distinct band-and k-dependence. This is supported by quasiparticle GW calculations performed within the framework of linearized muffin-tin orbitals. Our results suggest however that the GW approximation may be less accurate in the localized d-bands of Cu with their short-range charge fluctuations. We identify a connection of the self-energy behavior with the spatial localization of the one-electron wavefunctions in the unit cell and with their behavior in the core region. Mechanisms of this connection are discussed based on the local-density picture and on the non-local exchange interaction with the valence states.

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“…As for the determination of k ⊥ , which is not conserved but is also needed in order to map the electronic dispersion E(k) vs the total crystal wave vector k, a different approach is required. As a matter of fact, several specific experimental methods for absolute three dimensional band mapping have been developed [17,38,39], which however are rather complex and require additional and/or complementary experimental data. Alternatively, the value of k ⊥ can be determined if some a priori assumption is made for the dispersion of the electron final states involved in the photoemission process; in particular, one can either use the results of band structure calculations, or adopt a nearlyfree-electron description for the final bulk Bloch states:…”

Section: Kinematics Of Photoemissionmentioning

confidence: 99%

Probing the Electronic Structure of Complex Systems by ARPES

2004

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Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct methods of studying the electronic structure of solids. By measuring the kinetic energy and angular distribution of the electrons photoemitted from a sample illuminated with sufficiently high-energy radiation, one can gain information on both the energy and momentum of the electrons propagating inside a material. This is of vital importance in elucidating the connection between electronic, magnetic, and chemical structure of solids, in particular for those complex systems which cannot be appropriately described within the independent-particle picture. The last decade witnessed significant progress in this technique and its applications, thus ushering in a new era in photoelectron spectroscopy; today, ARPES experiments with 2 meV energy resolution and 0.2• angular resolution are a reality even for photoemission on solids. In this paper we will review the fundamentals of the technique and present some illustrative experimental results; we will show how ARPES can probe the momentum-dependent electronic structure of solids providing detailed information on band dispersion and Fermi surface, as well as on the strength and nature of those many-body correlations which may profoundly affect the one-electron excitation spectrum and, in turn, determine the macroscopic physical properties.

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Absolute Band Mapping by Combined Angle-Dependent Very-Low-Energy Electron Diffraction and Photoemission: Application to Cu

Cited by 71 publications

References 46 publications

Electronic excitations: density-functional versus many-body Green’s-function approaches

Electronic excitations: density-functional versus many-body Green’s-function approaches

Band- andk-dependent self-energy effects in the unoccupied and occupied quasiparticle band structure of Cu

Probing the Electronic Structure of Complex Systems by ARPES

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