Insights on the cuprate high energy anomaly observed in ARPES

Abstract

Recently, angle-resolved photoemission spectroscopy has been used to highlight an anomalously large band renormalization at high binding energies in cuprate superconductors: the high energy "waterfall" or high energy anomaly (HEA). The anomaly is present for both hole-and electron-doped cuprates as well as the half-filled parent insulators with different energy scales arising on either side of the phase diagram. While photoemission matrix elements clearly play a role in changing the aesthetic appearance of the band dispersion, i.e. creating a "waterfall"-like appearance, they provide an inadequate description for the physics that underlies the strong band renormalization giving rise to the HEA. Model calculations of the single-band Hubbard Hamiltonian showcase the role played by correlations in the formation of the HEA and uncover significant differences in the HEA energy scale for hole-and electron-doped cuprates. In addition, this approach properly captures the transfer of spectral weight accompanying doping in a correlated material and provides a unifying description of the HEA across both sides of the cuprate phase diagram. We find that the anomaly demarcates a transition, or cross-over, from a quasiparticle band at low binding energies near the Fermi level to valence bands at higher binding energy, assumed to be of strong oxygen character. Advancements in angle-resolved photoemission spectroscopy, an important probe of electronic structure, [1] have impacted significantly the study of strongly correlated materials. High resolution experiments, at binding energies up to 1 eV and higher, made possible by these advances, have revealed the presence of a "waterfall"-like structure with a characteristic kink at intermediate binding energies -the high energy anomaly (HEA) -in the dispersion of high T c superconductors. [2-12] Found universally in hole-doped compounds, the characteristic HEA energy scale is ∼ 300 meV with a similar dispersion anomaly observed in the half-filled parent insulators.[13] In contrast to earlier low energy studies focusing on dispersion kinks under ∼ 100 meV, [14] interpreted as signatures of coupling to low energy bosonic modes, [15-17] the extrapolated band bottom has a value larger than that obtained from band structure calculations [2, 3] and the energy scale associated with the anomaly would tend to rule-out coupling to similar bosonic modes as the origin of the HEA.More recently, anomalies have been found in electrondoped compounds at approximately twice the energy scale.[9-12] Taken together with results from hole-doped and half-filled parent materials, these findings raise questions about the origin or mechanism of the HEA, given the ap- Photoemission matrix elements clearly play a role in modifying the appearance of the HEA, complicating the analysis. The kink-or "waterfall"-like structure found in the first Brillouin zone (BZ) in experiments performed using synchrotron sources appears instead in newer experiments performed using low photon energy, laser sources as a ban...

Investigation of particle-hole asymmetry in the cuprates via electronic Raman scattering

“…On the whole, the evolution of the QPB qualitatively agrees with the results of ARPES experiments on hole-doped compounds, [37][38][39][40][41] including the evolution of spectral intensity and changes in momentum space position and robustness of this "waterfall"-like appearance as a function of momentum as found in previous work on the single-particle bandstructure. 22,35,[42][43][44][45][46] Figure 3 shows the spectral function for an electrondoped system with model parameters t ′ = −0.3t, µ = 2.0t, and β = 3.0/t near optimal electron-doping (∼ 15%). The LHB, centered at ∼ −6 t, has been reduced in intensity from spectral weight transfer into the QPB which now disperses down across the Fermi level from the precursor in the UHB.…”

High-energy anomaly in Nd2−xCexCuOSchmitt1, Moritz2, Johnston3 et al. 2011Phys. Rev. BSelf Cite9560View full textAdd to dashboardCite

“…4, none of the data display both features simultaneously, potentially due to their weak intensity. From QMC simulations, 18,30 we believe that the latter, dispersionless feature is actually a remnant of the QPB and its faintness likely stems from matrix element effects. 18,23 The dichotomy in energy scales originates from the presence of the charge-transfer gap -or Mott gap in the case of the single-band Hubbard QMC simulations done here -located on the unoccupied or occupied side of the Fermi level.…”

“…Previous quantum Monte Carlo (QMC) work concentrating on band structure differences throughout the BZ for optimal, or near optimal, h-and e-doping, 18,30 and other work based on a cluster extension of dynamical mean field theory (DMFT) concentrating on momentum and doping dependence 31 indicated that the key features of the HEA can be captured by the strongly correlated, single-band Hubbard model through a substantial renormalization of the underlying bandsturcture due to strong electron-electron correlations that give rise to a coherent, shallow quasiparticle band (QPB) at low binding energy in these systems. The relevant Mott-Hubbard physics captured by this model already is believed to be substantially universal in the HTSCs providing an effective low energy theory.…”

High-Energy Anomaly in the Angle-Resolved Photoemission Spectra ofNd2−xCexCuO4:

“…This difference was interpreted in terms of a shift of the chemical potential [14]. The experimental studies were accompanied by numerous theoretical papers [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].For the phenomenon of the HEA, a number of explanations have been suggested including Mott-Hubbard models with a transition from the coherent quasi-particle dispersion to the incoherent lower Hubbard band [5,18,21,26,32], a disintegration of the low-energy branch into a holon and spinon band due to a spin charge separation [2], a coupling to spin fluctuations [9,17,19,29,33], a coupling to phonons [7], string excitations of spinpolarons [32], a bifurcation of the quasi-particle band due to an excitation of a bosonic mode of charge 2e [22], and a coupling to plasmons [16]. These are all intrinsic interpretations in terms of many-body interactions leading to a change of the spectral function.…”

“…This difference was interpreted in terms of a shift of the chemical potential [14]. The experimental studies were accompanied by numerous theoretical papers [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”