Kinks in the dispersion of strongly correlated electrons

Abstract

The properties of condensed matter are determined by single-particle and collective excitations and their interactions. These quantum-mechanical excitations are characterized by an energy E and a momentum \hbar k which are related through their dispersion E_k. The coupling of two excitations may lead to abrupt changes (kinks) in the slope of the dispersion. Such kinks thus carry important information about interactions in a many-body system. For example, kinks detected at 40-70 meV below the Fermi level in the electronic dispersion of high-temperature superconductors are taken as evidence for phonon or spin-fluctuation based pairing mechanisms. Kinks in the electronic dispersion at binding energies ranging from 30 to 800 meV are also found in various other metals posing questions about their origins. Here we report a novel, purely electronic mechanism yielding kinks in the electron dispersions. It applies to strongly correlated metals whose spectral function shows well separated Hubbard subbands and central peak as, for example, in transition metal-oxides. The position of the kinks and the energy range of validity of Fermi-liquid (FL) theory is determined solely by the FL renormalization factor and the bare, uncorrelated band structure. Angle-resolved photoemission spectroscopy (ARPES) experiments at binding energies outside the FL regime can thus provide new, previously unexpected information about strongly correlated electronic systems.Comment: 8 pages, 5 figure

Anisotropic breakdown of Fermi liquid quasiparticle excitations in overdoped La2−xSrxCuO4

“…This may explain why no traces of superconductivity was found even though the measurement were carried out at T bulk Kramers-Kronig transforming ImS yields the real part of the self-energy ReS and hence the quasiparticle residue Z (1 À qReS/qo) À 1 . In the most simple case where l and F ¼ 1 are constants, Zpo c is found 11,13 . This leads to the KadowakiWoods relation 11,13 (Z À 2 $ l=o 2 c ) between the quasiparticle residue Z and the electron scattering amplitude l=o 2 c .…”

“…The Fermi liquid breakdown then appears as the cutoff energy o c vanishes although the electron coupling constant l and the a priori unknown function F remain constant. There exist relatively few studies of non-local Fermi liquids [13][14][15][16] . CeCoIn 5 is an example of a three-dimensional multi-band material that may have a directional breakdown 17,18 .…”

Dynamical Mean-Field Theory

“…Above ω the dispersion is given by a different renormalization with a small offset, E k = Z CP k + const, where Z CP is the weight of the central peak of A(ω). This theory explains kinks in the slope of the dispersion as a direct consequence of the electronic interaction [68]. The same mechanism may also lead to kinks in the low-temperature electronic specific heat [69].…”

“…Interestingly, for any typical spectral function A(ω) with three peaks, Kramers-Kronig relations and the DMFT self-consistency equations imply that the self-energy Σ(ω) abruptly changes slope inside the central peak at some frequency ω [68], once at positive and once at negative frequency. While this behavior is not visible in A(ω) itself, it leads to "kinks" in the effective dispersion relation E k of one-particle excitations, which is defined as the frequency for which the momentum-resolved spectral function A(k, ω) = −ImG(k, ω)/π = −(1/π) Im[1/(ω+µ− k −Σ(ω))] is maximal.…”

“…This energy cannot be obtained within FL theory itself. Namely, it is determined by Z FL and the non-interacting DOS, e.g., ω = 0.41Z FL D, where D is an energy scale of the non-interacting system such as half the bandwidth [68]. Above ω the dispersion is given by a different renormalization with a small offset, E k = Z CP k + const, where Z CP is the weight of the central peak of A(ω).…”