Theory of (001) surface and bulk states in Y$_{1-y}$Ca$_y$Ba$_2$Cu$_3$O$_{7-\delta}$}

TL;DR

This paper develops a self-consistent theoretical model for the surface and bulk electronic states of thin YCaBaCuO films, explaining experimental photoemission and tunneling data, and highlighting differences between surface and bulk properties.

Contribution

It introduces a comprehensive model incorporating Coulomb interactions and band structure constraints to accurately describe surface and bulk states in YCBCO, aligning with experimental observations.

Findings

Surface states differ qualitatively from bulk states and are doping-sensitive.

Calculated spectral functions match photoemission experiments closely.

Density of states features previously linked to competing order are explained by band effects.

Abstract

A self-consistent model is developed for the surface and bulk states of thin Y_{1-y}Ca_yBa_2Cu_3O_{7-\delta} (YCBCO) films. The dispersions of the chain and plane layers are modelled by tight-binding bands, and the electronic structure is then calculated for a finite-thickness film. The dopant atoms are treated within a virtual crystal approximation. Because YCBCO is a polar material, self-consistent treatment of the long range Coulomb interaction leads to a transfer of charge between the film surfaces, and to the formation of surface states. The tight binding band parameters are constrained by the requirement that the calculated band structure of surface states at CuO$_2$-terminated surfaces be in agreement with photoemission experiments. The spectral function and density of states are calculated and compared with experiments. Unlike the case of Bi_2Sr_2CaCu_2O_8, where the surfaces are believed to be representative of the bulk, the densities of states at the YCBCO surfaces are shown to be qualitatively different from the bulk, and are sensitive to doping. The calculated spectral function agrees closely with both bulk-sensitive and surface-sensitive photoemission results, while the calculated density of states for optimally-doped YCBCO agrees closely with tunneling experiments. We find that some density of states features previously ascribed to competing order can be understood as band structure effects.