Localization and orbital selectivity in iron-based superconductors with Cu substitution

Liu, Yang; Liu, Dayong; Wang, Jianglong; Sun, Jian; Song, Yaru; Zou, Liang‐Jian

doi:10.1103/physrevb.92.155146

Cited by 14 publications

(19 citation statements)

References 62 publications

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“…To precisely study the real-space fluctuations introduced by Cu substitution, we develop a realspace Green's function method by extending the Hubbard-I approximation [32] to the multiorbital Hubbard model. Our decoupling approximation has been proved to be adequate for the study of Cu-substituted ironbased superconductors [33]. In according with the prediction of other theoretical studies [7,8,10], we find an OSMP tuned by the Hund's rule coupling in the undoped cases, where the d xy orbital is a Mott insulator while…”

Section: Introductionsupporting

confidence: 86%

“…An inhomogeneous three-orbital Hubbard model is introduced for the Cu-substituted Fe-based compounds based on the local density functional calculations of -NaFe Cu As x x 1 [33], where a certain percentage of Fe sites is replaced by Cu ions randomly. The Hamiltonian is expressed as The values of the tight-binding (TB) model parameters were determined by the first principle calculations of the undoped Fe-based compounds [34,35].…”

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

“…The local density function calculation predicted that the Fermi surfaces of NaFe -x 1 Cu x As are mainly composed by three Fe 3d orbitals, i.e. d xy , d xz and d yz orbitals, whereas Cu 3d orbitals distribute from −4 to −2 eV, which is far below the Fermi level [33]. Therefore, the Fermi surfaces should be very sensitive to the hopping terms within the three Fe 3d orbitals.…”

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

“…In table 1, we display the details about the definitions of the intraorbital and interorbital hoping integrals a b T i j , for d xy , d xz and d yz orbitals of Fe ions. Further details about the model parameters can also be found in [33].…”

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

“…Although the correlations in various iron-based compounds are different, it is generally believed that the correlations should be smaller than the bandwidths. The parameters of the intraorbital and interorbital interactions of the three-orbital Hubbard model (equation (1)) have been obtained by the best fitting of the Fermi surfaces with the experimental result of LiFeAs [36], that is U = 1.5 eV and ¢ U = 1.125 eV [33]. However, some study also suggested that the Hund's rule coupling in iron-based superconductors should be within U 10 and U 5 [6].…”

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

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Orbital-selective Mott phase of Cu-substituted iron-based superconductors

2016

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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 orbitalselective 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 d xy orbital. We also find that more and more electronic states appear inside that Mott gap of the d xy 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 orbitalselective insulating phase, as a result of the cooperative effect of the Hund's rule coupling and the impurity-induced disorder. the d d xz yz orbitals remain itinerant. In the presence of the Cu substitution, the competition between the Mott-Hubbard and Anderson metal-insulator transitions (MIT) is reveled by the study of the interplay between the Hund's rule coupling and the impurity-induced disorder in Cu-substituted Fe-based superconductors. We find that the Cu substitutions can introduce some states inside the Mott gap of the d xy orbital around the Fermi level, which can be suppressed by the increasing Hund's rule coupling. As a result, the increase of the critical value for the Mott-Hubbard MIT transition is found in the d xy orbital. Meanwhile, the degenerate d d xz yz orbitals are Anderson localized, indicating the existence of an orbital-selective insulating phase in Fe-based superconductors with the presence of impurities. We also construct a complete phase diagram for Cu-substituted iron-based superconductors, depended on both the Hund's rule coupling and the concentration of Cu impurities.The paper is organized as follows. In section 2, we introduce an inhomogeneous three-orbital Hubbard model, and develop a real-space Green's function approach to study the cooperative effect of disorder and multiorbital correlation in Cu-substituted Fe-based superconductors. In section 3, we first show the orbitalselective Mott transition (OSMT) introduced by the Hund's rule coupling in undoped compound. Then we study the cooperative effect of the Hund's rule coupling and impurity-induced disorder on the phase transitions in Cu-substituted iron-based superconductors. Further, a phase diagram is obtained by the study of the competition between the Mott-Hubbard and Anderson MITs. The principal findings of this paper are summarized in section 4.

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Section: Introductionsupporting

confidence: 86%

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

Section: Model Hamiltonian and Methodologymentioning

confidence: 99%

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Orbital-selective Mott phase of Cu-substituted iron-based superconductors

2016

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Disorder-driven electron delocalization in strange metals: The case of tetragonal FeTe

Craco

2017

Solid State Communications

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Fluctuating magnetism of Co- and Cu-doped NaFeAs

Pelliciari

Ishii

Xing

et al. 2021

Applied Physics Letters

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We report an x-ray emission spectroscopy (XES) study of the local fluctuating magnetic moment (µ bare ) in NaFe 1−x Co x As and NaFe 1−x Cu x As. In NaFeAs, the reduced height of the As ions induces a local magnetic moment higher than Ba 2 As 2 , despite lower T N and ordered magnetic moment. As NaFeAs is doped with Co µ bare is slightly reduced, whereas Cu doping leaves it unaffected, indicating a different doping mechanism: based on electron counting for Co whereas impurity scattering dominates in the case of Cu. Finally, we observe an increase of µ bare with temperature in all samples as observed in electron-and hole-doped BaFe 2 As 2 . Since both Co and Cu doping display superconductivity, our findings demonstrate that the formation of Cooper pairs is not connected with the complete loss of fluctuating paramagnetic moments.The structure of superconducting Fe pnictides is composed of FeAs layers separated by spacing ions where Fe occupies a four-fold coordination site with a tetrahedral environment of As ions as depicted in Fig. 1(a). This coordination can alternatively be seen as an Fe checkerboard layer with As ions at the center of every single Fe square alternating above and below it, as illustrated in Fig. 1 (b).A key parameter for the magnetism of Fe pnictides is the height (h) of the As ions with respect to the Fe layer (Fig. 1(b)) 1-7 . In NaFeAs, the large h (1.416 Å) induces magnetic frustration compared to BaFe 2 As 2 (1.358 Å) 1 , leading to the reduction of the ordered magnetic moment and T N (see Table I for the respective values). 1,4,5,[8][9][10] . Despite the reduced ordered moment, the spin excitations of NaFeAs have been detected by both inelastic neutron scattering (INS) and resonant inelastic x-ray scattering (RIXS) 1,3,5 , and from the integration in energy and momentum spaces of the INS signal a fluctuating magnetic moment higher than BaFe 2 As 2 has been quantified 1 . These evidences are a clear demonstration of the importance of magnetic fluctuations in the NaFeAs (111) series.A peculiarity of Fe pnictides, in respect to the cuprates, is the high flexibility to achieve SC through different types of doping. Fe pnictides can be electron-, hole-, or isovalent-doped with SC emerging in all the cases 6,9-12 . The doping flexibility is not only limited to the type of carriers (electrons or holes) but also to the site of the dopant atoms. Dopants can be placed in all the structural sites: the spacing layer (e.g. Ba 1−x K x Fe 2 As 2 ), the Fe layer (e.g. NaFe 1−x Co x As), and the As layer [e.g. BaFe 2 (As 1−x P x ) 2 ] 6,9-12 . The effect of doping transition

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Localization and orbital selectivity in iron-based superconductors with Cu substitution

Cited by 14 publications

References 62 publications

Orbital-selective Mott phase of Cu-substituted iron-based superconductors

Orbital-selective Mott phase of Cu-substituted iron-based superconductors

Disorder-driven electron delocalization in strange metals: The case of tetragonal FeTe

Fluctuating magnetism of Co- and Cu-doped NaFeAs

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