Spectral function tour of electron-phonon coupling outside the Migdal limit

Abstract. 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. Among the various classes of complex systems, of great interest are the transition metal oxides, which have been at the center stage in condensed matter physics for the last four decades. Following a general introduction to the topic, we will lay the theoretical basis needed to understand the pivotal role of ARPES in the study of such systems. After a brief overview on the state-of-the-art capabilities of the technique, we will review some of the most interesting and relevant case studies of the novel physics revealed by ARPES in 3d -, 4d -and 5d -based oxides.

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“…This is illustrated with the second example discussed here, the one-dimensional (1D) Holstein model [74], shown in Fig. 1.13.…”

Section: Electron-phonon Correlations In Solids: the Polaronmentioning

confidence: 82%

ARPES: A Probe of Electronic Correlations

Comin

Damascelli

2014

Springer Series in Solid-State Sciences

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“…The latter is usually taken to depend only on energy, as its momentum dependence is considered weak. 22 If a cut at a given energy E = E m (momentum distribution curve) is made out of a two-dimensional map A(k, E), nearly Lorentzian lineshape is obtained with a maximum at k m such that…”

Section: Methodsmentioning

confidence: 99%

“…Different approaches based on self-consistent procedures have been developed to determine the bare band, self-energy and ultimately, electronphonon coupling strength. 15,21,22 A self-consistent method has already been applied to the photoemission data of potassium doped graphene on Ir(111). 15 Several aspects of the low-energy quasiparticle dynamics were addressed: renormalization of the π * band close to the Fermi level due to the coupling to phonons; phonon spectrum associated with the renormalization; the width of spectral lines in connection with the electron scattering rate.…”

Section: Introductionmentioning

confidence: 99%

Finding the bare band: Electron coupling to two phonon modes in potassium-doped graphene on Ir(111)

et al. 2012

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We analyze renormalization of the π * band of n-doped epitaxial graphene on Ir(111) induced by electronphonon coupling. Our procedure of extracting the bare band relies on recursive self-consistent refining of the functional form of the bare band until the convergence. We demonstrate that the components of the self-energy, as well as the spectral intensity obtained from angle-resolved photoelectron spectroscopy (ARPES) show that the renormalization is due to the coupling to two distinct phonon excitations. From the velocity renormalization and an increase of the imaginary part of the self-energy we find the electron-phonon coupling constant to be ∼ 0.2, which is in fair agreement with a previous study of the same system, despite the notable difference in the width of spectroscopic curves. Our experimental results also suggest that potassium intercalated between graphene and Ir(111) does not introduce any additional increase of the quasiparticle scattering rate.

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“…To overcome this difficulty, the self-consistency of the self-energy via Kramers-Kronig relation is the most widely used criteria to extract the self-energy25678. Moreover, iterative fitting algorithms for the determination of the bare band have also been developed based on the maximum entropy method91011 or the Kramers-Kronig relation121314. In contrast, many previous ARPES experiments have regarded the bare band as a renormalized band due to the electron-electron coupling, which has enabled evaluation of the ‘effective’ bosonic self-energy and coupling strength2345678.…”

mentioning

confidence: 99%

‘True’ bosonic coupling strength in strongly correlated superconductors

Iwasawa

Yoshida

Hase

et al. 2013

Sci Rep

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Clarifying the coupling between electrons and bosonic excitations (phonons or magnetic fluctuations) that mediate the formation of Cooper pairs is pivotal to understand superconductivity. Such coupling effects are contained in the electron self-energy, which is experimentally accessible via angle-resolved photoemission spectroscopy (ARPES). However, in unconventional superconductors, identifying the nature of the electron-boson coupling remains elusive partly because of the significant band renormalization due to electron correlation. Until now, to quantify the electron-boson coupling, the self-energy is most often determined by assuming a phenomenological 'bare' band. Here, we demonstrate that the conventional procedure underestimates the electron-boson coupling depending on the electron-electron coupling, even if the self-energy appears to be self-consistent via the Kramers-Kronig relation. Our refined method explains well the electron-boson and electron-electron coupling strength in ruthenate superconductor Sr 2 RuO 4 , calling for a critical revision of the bosonic coupling strength from ARPES self-energy in strongly correlated electron systems.T he many-body effects, the coupling between electrons and various excitations, are contained in the electron self-energywhich is accessible via the spectral function A(k, v) measured by angle-resolved photoemission spectroscopy (ARPES) aswhere e 0 (k) is the non-interacting (bare) energy-band dispersion and the real and imaginary parts of the selfenergy, . However, the derivation of the self-energy depends on the unfounded assumption of a bare band, which cannot be directly observed. To overcome this difficulty, the self-consistency of the self-energy via Kramers-Kronig relation is the most widely used criteria to extract the self-energy 2,[5][6][7][8] . Moreover, iterative fitting algorithms for the determination of the bare band have also been developed based on the maximum entropy method 9-11 or the Kramers-Kronig relation [12][13][14] . In contrast, many previous ARPES experiments have regarded the bare band as a renormalized band due to the electron-electron coupling, which has enabled evaluation of the 'effective' bosonic self-energy and coupling strength [2][3][4][5][6][7][8] . However, the term 'effective' is often abbreviated or overlooked in many cases, although it has been proposed that the effective electron-boson coupling strength is smaller than the true coupling strength because of the electron-electron coupling 15,16 . There is a need, therefore, to reconsider and/or refine the most commonly used method for extracting the bosonic self-energy from ARPES data. ResultsWe assume two main scattering channels, the electron-boson and electron-electron couplings. The energy-scales associated with these two are quite different: the electron-boson coupling dominates at low energy-scales (at most ,100 meV), whereas the electron-electron coupling over a wide energy-scale (eV-order). The two are thus nearly independent in the scattering process and hence the Matth...

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Spectral function tour of electron-phonon coupling outside the Migdal limit

Cited by 11 publications

References 45 publications

ARPES: A Probe of Electronic Correlations

ARPES: A Probe of Electronic Correlations

Finding the bare band: Electron coupling to two phonon modes in potassium-doped graphene on Ir(111)

‘True’ bosonic coupling strength in strongly correlated superconductors

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