The mechanisms of superconductivity in high-temperature superconductors have been extensively studied using various two-dimensional
models of electronic interactions.
The CuO2 plane in cuprates plays an important role for the appearance of superconductivity.
It is well known that the parent materials are a Mott insulator and the hole doping leads to superconductivity.
A Mott insulator is an insulator where the metallic conductivity is lost due to the strong correlation between
electrons.
Here we present the results on the Mott transition of high temperature cuprates at half-filling.
In the case of cuprates the insulating state is regarded as a charge-transfer insulator,
We proposed a wave function of Mott state on the basis of an improved Gutzwiller function.
The Mott transition was examined by using the Gutzwiller-projected wave function with doublon-holon correlation.
The energy of the wave function is not, however, so lowered only by considering the doublon-holon correlation.
We improved the wave function, so that the variational energy is considerably improved compared to the
wave function with only Jastrow and doublon-holon correlation factors.
The Gutzwiller wave function is given as ψG = PGψ0 where
PG is the Gutzwiller operator and controls the on-site electron correlation. ψ0
is a one-particle wave function such as the Fermi sea or the Hartree-Fock state with some ordering.
We consider an improved wave function starting from the Gutzwiller function given by
ψ = exp(λK)ψG,
where K is the kinetic part of the Hamiltonian and λ ia a variational parameter.
We can further improve the wave function by multiplying PG and exponential factor again
such as ψ(3) = PGe-λKPGψ0.
The above wave function can be regarded as a wave function for the Mott state of the Hubbard model [1].
References:
[1] T. Yanagisawa and M. Miyazaki: EPL 107, 27004 (2014).
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