Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Green's function variational approach to orbital polarons in KCuF3   We develop an $e_g$ orbital, $t$-$J$-like model of a single charge doped into
a two-dimensional plane with ferromagnetic spin order and alternating orbital
order, and present its solution by Green's functions in the variational
approximation framework. The model is designed to represent the orbital physics
within ferromagnetic $(a,b)$ planes of KCuF$_3$ and K$_2$CuF$_4$. The
variational approximation (VA) relies on the systematic generation of equations
of motion for the Green's function, taking into account the real-space
constraints coming from the exclusion of doubly occupied sites. This method is
compared to the firmly established self-consistent Born approximation, and to
the variational cluster approximation (VCA) which relies on the itinerant
regime of the model. We find that the present variational approximation
captures the essential aspects of the spectral weight distribution of the
coherent quasiparticle state and gives a result similar to the VCA, while also
reproducing well the momentum dependence of the spectral moments. In contrast,
the spectral function obtained within the self-consistent Born approximation is
more incoherent and its quasiparticle is heavier, at strong effective
couplings, than observed with VCA and VA.

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The categories of this paper are: dg-ga
36
The categories of this paper are: cmp-lg
3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
1
The categories of this paper are: cs
16
The categories of this paper are: stat