Evolution of Midgap States and Residual Three Dimensionality inLa2−xSrxCuO4

Abstract

We carry out extensive first-principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La2-xSrxCuO4 over a wide range of binding energies. Intercell hopping and the associated three dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g., the presence of a lower Hubbard band coexisting with midgap states in the doped insulator), a number of salient features of the experimental ARPES spectra are captured to a surprising extent when kz dispersion is properly included in the analysis.

Role of site selectivity, dimensionality, and strong correlations in angle-resolved photoemission from cuprate superconductors

“…As a prelude to the ARPES intensity computations, the fully self-consistent electronic structures of the undoped parent compounds La 2 CuO 4 (LCO), Nd 2 CuO 4 (NCO), and Bi2212 were obtained within the LDA by using the well-established all electron Kohn-Korringa-Rostoker (KKR) Green function methodology [28,29]; our band structures and FSs are in reasonable accordance with the published data [9,21,30]. Following common practice, the metallic state obtained by doping is assumed to be described by these LDA generated metallic band structures.…”

“…The nodal region on the other hand, where the k z -dispersion is small, undergoes little change. The projection of the FS on to the (0 0 1)-plane in (b) gives the region of allowed transitions in ARPES [20,21]. In other words, the FS map measured in ARPES is intrinsically broadened due to the effect of k z -dispersion so as to be contained within the boundaries set by the projection of (b), aside from the effects of resolution and the finite lifetimes of the initial and final states.…”

“…The effect of O doping or of La/Sr or Nd/Ce substitution is mainly to adjust the electron concentration and, therefore, we have modelled the doped compounds at any given doping level x by implicitly invoking a rigid band filling of the band structure with the appropriate number of electrons per unit cell. The crystal potentials used are the same as those employed in our previous studies of Bi2212, LSCO and NCCO [9,15,21,30].…”

“…The ARPES intensities were computed within the one-step photoemission formalism, assuming a BiO or a LaO layer terminated [31] surface for Bi2212 and LSCO, respectively; see, e.g., [9,15,20,21] for details. The results on NCCO are for the CuO 2 -Nd-O 2 -Nd terminated surface, which generally appears to be the most representative of the experimental spectra [32].…”

“…In a 3D material, at a fixed value of k , k zdispersion leads to shifts in the position of the ARPES peak with photon energy (hν) [17]- [19]. The behaviour in a quasi-2D system is fundamentally different in that the spectral peaks will generally not shift with hν, but will instead display an irreducible linewidth which is a function of the in-plane momentum k [20,21]. This reflects the loss of k z -selectivity in the underlying photoexcitation process when the final-state damping, which is typically of the order of eVs, becomes much larger than the energy scale of the initial-state dispersion.…”