The Green function variational approximation: Significance of physical constraints

Abstract

We present a calculation of the spectral properties of a single charge doped at a Cu($3d$) site of the Cu-F plane in KCuF${}_3$. The problem is treated by generating the equations of motion for the Green's function by means of subsequent Dyson expansions and solving the resulting set of equations. This method, dubbed the variational approximation, is both very dependable and flexible, since it is a systematic expansion with precise control over elementary physical processes. It allows for deep insight into the underlying physics of polaron formation as well as for inclusion of many physical constraints, such as excluding crossing diagrams and double occupation constraint, which are not included in the Self-Consistent Born Approximation. Here we examine the role and importance of such constraints by analyzing various spectral functions obtained in second order VA.

5 pages, 1 figure

References in corpus (6)

• Absence of Hole Confinement in Transition Metal Oxides with Orbital Degeneracy
• The dynamics of a doped hole in cuprates is not controlled by spin fluctuations
• Ferro-Orbitally Ordered Stripes in Systems with Alternating Orbital Order
• Spin-Orbital Order Modified by Orbital Dilution in Transition Metal Oxides: From Spin Defects to Frustrated Spins Polarizing Host Orbitals
• Green's function variational approach to orbital polarons in KCuF3
• Quantum versus classical polarons in a ferromagnetic CuO${}_3$-like chain