Abstract
We study the phase transition in Cu-substituted iron-based superconductors with a new developed real-space Green’s function method. We find that Cu substitution has strong effect on the orbital-selective Mott transition introduced by the Hund’s rule coupling. The redistribution of the orbital occupancy which is caused by the increase of the Hund’s rule coupling, gives rise to the Mott–Hubbard metal-insulator transition in the half-filled dxy orbital. We also find that more and more electronic states appear inside that Mott gap of the dxy orbital with the increase of Cu substitution, and the in-gap states around the Fermi level are strongly localized at some specific lattice sites. Further, a distinctive phase diagram, obtained for the Cu-substituted Fe-based superconductors, displays an orbital-selective insulating phase, as a result of the cooperative effect of the Hund’s rule coupling and the impurity-induced disorder.
Highlights
The multiorbital nature of iron pnictides and chalcogenides is essential for understanding the mechanism of the high-temperature superconductivity of iron-based superconductors [1, 2]
It has been demonstrated by the dynamical mean-field theory (DMFT) [15] that, in a multiorbital system, the orbital-selective Mott phase (OSMP) is usually derived from three possible reasons: (1) the bandwidths of the two orbitals are significantly different [16]; (2) the influence of the crystal-field splitting is considerable [17]; and (3) the orbital degeneracy is reduced owing to the distinct features of the orbitals or by some other reasons [18, 19]
It is obvious that the electron transition from the dxz/dyz orbitals to dxy orbital plays an essential role in finding the OSMP
Summary
The multiorbital nature of iron pnictides and chalcogenides is essential for understanding the mechanism of the high-temperature superconductivity of iron-based superconductors [1, 2]. Strong orbital-dependence of the correlation was found in iron chalcogenides [11], and the signs of the appearance of OSMP were observed in AxFe2−ySe2 (A=K, Rb) at high temperature [12, 13, 14] It has been demonstrated by the dynamical mean-field theory (DMFT) [15] that, in a multiorbital system, the OSMP is usually derived from three possible reasons: (1) the bandwidths of the two orbitals are significantly different [16]; (2) the influence of the crystal-field splitting is considerable [17]; and (3) the orbital degeneracy is reduced owing to the distinct features of the orbitals or by some other reasons [18, 19].
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