Effect of 3d doping on the electronic structure of BaFe<sub>2</sub>As<sub>2</sub>

McLeod, John A.; Buling, Anna; Green, R. J.; Boyko, Teak D.; Skorikov, N. A.; Kurmaev, E.Z.; Neumann, M.; Finkelstein, L. D.; Ni, N.; Thaler, A.; Bud’ko, Sergey L.; Canfield, Paul C.; Moewes, A.

doi:10.1088/0953-8984/24/21/215501

Cited by 42 publications

(69 citation statements)

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“…Since Cu 3d states are located deeper below the E F than Co, 6,9,45 the extra d electrons for Cu almost totally locate around the substituted site. Hence, closed 3d shell is observed by XPS and XAS, although there is a little delocated electron introduced by Cu dopant.…”

Section: Discussionmentioning

confidence: 99%

“…X-ray photoelectron spectroscopy (XPS) and x-ray absorption (XAS) measurements show that Cu 3d states locate at the bottom of the valence band in a localized 3d 10 shell, so that the formal valence state of Cu is +1 and the substitution of Fe 2+ by Cu 1+ results in hole doping. [7][8][9] The theoretical and experimental studies on SrCu 2 As 2 , the end member of Sr(Fe 1−x Cu x ) 2 As 2 series, indicate that it is an sp-band * Corresponding author; Electronic address: chenxh@ustc.edu.cn metal with hole-type carries dominate and Cu in the nonmagnetic 3d 10 electronic configuration corresponds to the valence state Cu 1+ , 7,10,11 which further supports the result of XPS and XAS. In addition, the doping effect of Cu is similar to that of Mn, which is also considered as hole doping and no superconductivity has been found.…”

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confidence: 99%

“…The deviation can be explained that part of the doped electrons fill the impurity band which is located deep below the Fermi level (E F ) and do not fill the energy bands as predicted by the rigid-band model. 6,9 II. EXPERIMENTAL DETAILS A series of NaFe 1−x Cu x As single crystals was grown by adopting the NaAs flux method.…”

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Phase diagram and physical properties of NaFe1−xCuxAs single crystals

et al. 2013

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A series of high quality NaFe1−xCuxAs single crystals has been grown by a self-flux technique, which were systematically characterized via structural, transport, thermodynamic, and high pressure measurements. Both the structural and magnetic transitions are suppressed by Cu doping, and bulk superconductivity is induced by Cu doping. Superconducting transition temperature (Tc) is initially enhanced from 9.6 to 11.5 K by Cu doping, and then suppressed with further doping. A phase diagram similar to NaFe1−xCoxAs is obtained except that insulating instead of metallic behavior is observed in extremely overdoped samples. Tc's of underdoped, optimally doped, and overdoped samples are all notably enhanced by applying pressure. Although a universal maximum transition temperature (T max c ) of about 31 K under external pressure is observed in underdoped and optimally doped NaFe1−xCoxAs, T max c of NaFe1−xCuxAs is monotonously suppressed by Cu doping, suggesting that impurity potential of Cu is stronger than Co in NaFeAs. The comparison between Cu and Co doping effect in NaFeAs indicates that Cu serves as an effective electron dopant with strong impurity potential, but part of the doped electrons are localized and do not fill the energy bands as predicted by the rigid-band model.

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Section: Discussionmentioning

confidence: 99%

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Phase diagram and physical properties of NaFe1−xCuxAs single crystals

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“…100 Resonant and nonresonant x-ray absorption and emission spectroscopy measurements as well as core and valence level x-ray photoelectron spectroscopy measurements were carried out by McLeod et al 101 on the Fe, Co, Ni and Cu atoms in Ba(Fe 1−x M x ) 2 As 2 crystals with M = Co, Ni and Cu. They found that there is little charge transfer from the dopant atoms to the Fe atoms and that the iron arsenides are not strongly correlated electron systems.…”

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confidence: 99%

Crystal growth and physical properties of SrCu2As2, SrCu2Sb
Anand
¹
,
Perera
²
,
Pandey
³

et al. 2012
Phys. Rev. B

107

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We report the growth of single crystals of SrCu2As2, SrCu2Sb2, SrCu2(As0.84Sb0.16)2 and BaCu2Sb2 using the self-flux technique and their structural, magnetic, thermal and transport properties that were investigated by powder x-ray diffraction (XRD), magnetic susceptibility χ, specific heat Cp and electrical resistivity ρ measurements versus temperature T from 1.8 to 350 K. Rietveld refinements of XRD patterns for crushed crystals confirm that SrCu2As2 crystallizes in the ThCr2Si2-type body-centered tetragonal structure (space group I4/mmm) and SrCu2Sb2 crystallizes in the CaBe2Ge2-type primitive tetragonal structure (space group P 4/nmm). However, as reported previously, BaCu2Sb2 is found to have a large unit cell consisting of three blocks. Here a ThCr2Si2-type block is sandwiched between two CaBe2Ge2-type blocks along the c-axis with an overall symmetry of I4/mmm, as reported, but likely with a monoclinic distortion. The χ data of all these compounds are diamagnetic and reveal nearly T -independent anisotropic behavior. The χ of SrCu2As2 is found to be larger in the ab-plane than along the c-axis, as also previously reported for pure and doped BaFe2As2, whereas the χ values of SrCu2Sb2 and BaCu2Sb2 are larger along the c-axis. This difference in anisotropy appears to arise from the differences between the crystal structures. The finite values of the Sommerfeld linear specific heat coefficients γ and the T dependences of ρ reveal metallic character of all four compounds. The electronic and magnetic properties indicate that these compounds are sp metals with Cu in the nonmagnetic 3d 10 electronic configuration corresponding to the oxidation state Cu +1 , as previously predicted theoretically for SrCu2As2 by D. J. Singh [Phys. Rev. B 79, 153102 (2009)]. We present a brief review of theoretical and experimental work on the doping character of transition metals for Fe in BaFe2As2. The As-As covalent interlayer bond distances in the collapsed-tetragonal (Ca,Sr,Ba)Cu2As2 compounds are much shorter than the nonbonding As-As distances in BaFe2As2. Thus the electronic character of the Cu and the strength of the As-As interlayer bonding are both expected to drastically change between weakly Cu-substituted BaFe2As2 and pure BaCu2As2, perhaps via a first-order lattice instability such as a miscibility gap in the Ba(Fe1−xCux)2As2 system.

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“…As the SDW magnetic character of the Fe 3d electrons is nearly unaffected by the magnetic field (not shown), we attribute this spin-dependent scattering mechanism to the Cu 2+ (s = 1/2) local moments shown by recent ESR experiments, which directly probe the Cu oxidation state [16]. The ESR data are in contrast to previous reports based on ARPES, XAS and NMR measurements, which suggest that the Cu atoms are in the Cu 1+ oxidation state [31,[34][35][36]. However, the data reported here is consistent with a Cu 2+ spin-dependent scattering mechanism.…”

Section: Resultsmentioning

confidence: 55%

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

Piva

Besser

Mydeen

et al. 2015

J. Phys.: Condens. Matter

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We report a combined study of external pressure and Cu-substitution on BaFe 2 As 2 single crystals grown by the in-flux technique. At ambient pressure, the Cu-substitution is known to suppress the spin density wave (SDW) phase in pure BaFe 2 As 2 (T SDW ≈ 140 K) and to induce a superconducting (SC) dome with a maximum transition temperature T max c 4.2 K. This T max c is much lower than the T c ∼ 15-28 K achieved in the case of Ru, Ni and Co substitutions. Such a lower T c is attributed to a Cu 2+ magnetic pair-breaking effect. The latter is strongly suppressed by applied pressure, as shown herein, T c can be significantly enhanced by applying high pressures. In this work, we investigated the pressure effects on Cu 2+ magnetic pair-breaking in the BaFe 2−x Cu x As 2 series. Around the optimal concentration (x opd = 0.11), all samples showed a substantial increase of T c as a function of pressure. Yet for those samples with a slightly higher doping level (over-doped regime), T c presented a dome-like shape with maximum T c 8 K. Remarkably interesting, the under-doped samples, e.g. x = 0.02 display a maximum pressure induced T c 30 K which is comparable to the maximum T c 's found for the pure compound under external pressures. Furthermore, the magnetoresistance effect as a function of pressure in the normal state of the x = 0.02 sample also presented an evolution consistent with the screening of the Cu 2+ local moments. These findings demonstrate that the Cu 2+ magnetic pair-breaking effect is completely suppressed by applying pressure in the low concentration regime of Cu 2+ substituted BaFe 2 As 2 .

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Effect of 3d doping on the electronic structure of BaFe₂As₂

Cited by 42 publications

References 43 publications

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

Crystal growth and physical properties of SrCu2As2, SrCu2Sb
Anand
¹
,
Perera
²
,
Pandey
³

et al. 2012
Phys. Rev. B

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals

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Effect of 3d doping on the electronic structure of BaFe2As2

Cited by 42 publications

References 43 publications

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

Phase diagram and physical properties of NaFe1−xCuxAs single crystals

Crystal growth and physical properties of SrCu2As2, SrCu2SbAnand1, Perera2, Pandey3 et al. 2012Phys. Rev. B

Combined external pressure and Cu-substitution studies on BaFe2As2single crystals

Contact Info

Product

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About

Effect of 3d doping on the electronic structure of BaFe₂As₂

Crystal growth and physical properties of SrCu2As2, SrCu2Sb
Anand
¹
,
Perera
²
,
Pandey
³

et al. 2012
Phys. Rev. B

Combined external pressure and Cu-substitution studies on BaFe₂As₂single crystals