Electronic structure in a one-Fe Brillouin zone of the iron pnictide superconductors ${\mathrm{CsFe}}_{2}{\mathrm{As}}_{2}$ and ${\mathrm{RbFe}}_{2}{\mathrm{As}}_{2}$

Electronic structure in a one-Fe Brillouin zone of the iron pnictide superconductors ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$

S. Kong, D. Y. Liu, S. T. Cui, S. L. Ju, A. F. Wang, X. G. Luo, L. J. Zou, X. H. Chen, G. B. Zhang, and Z. Sun

Phys. Rev. B 92, 184512 – Published 24 November 2015

Abstract

Using angle-resolved photoemission spectroscopy, we studied the electronic structures of ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$ . Contrary to other iron-based superconductors where the band structures are usually depicted in the two-Fe Brillouin zone (BZ), we found that the distribution of electronic spectral weight in ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$ follows the one-Fe BZ, and that the emerging band structure is qualitatively consistent with theoretical band calculations of the one-Fe BZ except for some shadow band effect. Our data suggest that the interlayer separation is an important tuning factor for the physics of FeAs layers, the increase of which can reduce the coupling between Fe and As and lead to the emergence of the electronic structure in accord with the one-Fe symmetry of the Fe square lattice. Our finding puts strong constraints on the theoretical models constructed on the basis of the one-Fe BZ.

Received 19 November 2014
Revised 15 September 2015

DOI:https://doi.org/10.1103/PhysRevB.92.184512

Authors & Affiliations

S. Kong¹, D. Y. Liu^2,*, S. T. Cui¹, S. L. Ju¹, A. F. Wang³, X. G. Luo^3,4, L. J. Zou², X. H. Chen^3,4, G. B. Zhang¹, and Z. Sun^1,4,†

¹National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People's Republic of China
²Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
³Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
⁴Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, People's Republic of China

^*[email protected]
^†[email protected]

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Vol. 92, Iss. 18 — 1 November 2015

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Figure 1
(a) A sketch of the Fe-As layer with As anions located above and below the Fe plane. The blue thick lines show the one-Fe unit cell of the primary Fe square lattice. The red dashed lines define the crystallographic two-dimensional unit cell with inequivalent Fe at the corners and the center. We note here that the Fe-Fe distance in real space is $a / \sqrt{2}$ , where $a$ is the lattice parameter. Their corresponding Brillouin zones in momentum space are referred to as the one-Fe BZ and two-Fe BZ, respectively. (b) The Brillouin zone of 122 iron-based superconductors. (c) Photoemission intensity mapping at the Fermi energy for ${CsFe}_{2} {As}_{2}$ taken with 85 eV and circular polarized photons. The blue and red squares illustrate the one-Fe BZ and two-Fe BZ, respectively. The dots indicate the $k_{F}$ positions determined by the peak positions of the momentum distribution curves, and the thin dashed lines show the Fermi surface pockets deduced from the $k_{F}$ positions. In the one-Fe BZ, there is one hole Fermi surface sheet around the zone center $Γ^{'}$ , one hole sheet near the middle point of the zone boundary $X^{'}$ or $Y^{'}$ , and one four-leaf-clover shaped pocket and one circular hole pocket around the zone corner $M^{'}$ . (d)–(f) Photoemission intensity plots along cuts no. 1, no. 2, and no. 3 in panel c, respectively. The dotted lines are guides for the eyes to trace the dispersions of near- $E_{F}$ electronic bands.
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Figure 2
(a,b) Fermi surface mappings of ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$ obtained using various photon energies, respectively. The data were measured at $T = 25$ K with circular-polarized photons. The blue solid lines and red dashed lines indicate the orientations of the one-Fe and two-Fe BZs, respectively. High-symmetry points in the one-Fe BZ are marked with a prime symbol. (c) A sketch of the Brillouin zones of the two-Fe (red dashed lines) and one-Fe (blue solid lines) scenarios. (d,e) The calculated momentum cuts for the two-Fe BZ along the green line in panel (b) with various photon energies for ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$ , respectively. An inner potential of 15 eV was used for the calculations.
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Figure 3
(a) The Fermi surface of ${CsFe}_{2} {As}_{2}$ determined by experimental data. The blue and red squares represent the one-Fe BZ and two-Fe BZ, respectively. The hatched areas indicate the locations of the $ɛ$ pockets in theoretical models based on the one-Fe BZ. (b) The band dispersions of ${CsFe}_{2} {As}_{2}$ in the one-Fe BZ, determined by Figs. 1–1. (c) The constructed Fermi surface in the two-Fe BZ by folding all bands with a vector of ( $π, π$ ) of the one-Fe BZ. The folding vector is indicated in panel (a).
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Figure 4
Fermi surface sheets of ${CsFe}_{2} {As}_{2}$ obtained by LDA calculations.
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Figure 5
(a) Orbital-resolved band structure of ${CsFe}_{2} {As}_{2}$ plotted along the high-symmetry lines for the two-Fe BZ. (b,c) The unfolded band structures in the one-Fe BZ, and (d,e) the corresponding Fermi surface topologies without and with glide mirror symmetries.
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Figure 6
( $a_{1}$ ),( $a_{2}$ ) The experimental setups with different photon polarizations along $Γ^{'} - X^{'}$ . ( $a_{3}$ ) The experimental setups with even photon polarizations along $Γ^{'} - M^{'}$ . The $x^{'}, k_{x}^{'}, y^{'}$ , and $k_{y}^{'}$ axes are along the neighboring Fe-Fe directions. The gray planes are mirror planes for the analyses of orbital symmetries. The pink arrows indicate the light polarizations. ( $b_{1}$ )–( $b_{3}$ ) The experimental Fermi surface mapping using the setups in panels ( $a_{1}$ )–( $a_{3}$ ), which were taken using 85 eV photons at $T = 25$ K. The blue solid lines and red dashed lines indicate the orientations of the one-Fe and two-Fe BZs, respectively. ( $c_{1}$ ),( $c_{2}$ ) Photoemission intensity plots taken along the $Γ^{'} - X^{'}$ cuts in panels ( $b_{1}$ ) and ( $b_{2}$ ), respectively. ( $c_{3}$ ) Photoemission intensity plots taken along the $Γ^{'} - M^{'}$ cuts in panel ( $b_{3}$ ).
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Physical Review B

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Electronic structure in a one-Fe Brillouin zone of the iron pnictide superconductors ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$

S. Kong, D. Y. Liu, S. T. Cui, S. L. Ju, A. F. Wang, X. G. Luo, L. J. Zou, X. H. Chen, G. B. Zhang, and Z. Sun

Phys. Rev. B 92, 184512 – Published 24 November 2015

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Electronic structure in a one-Fe Brillouin zone of the iron pnictide superconductors CsFe2As2 and RbFe2As2

S. Kong, D. Y. Liu, S. T. Cui, S. L. Ju, A. F. Wang, X. G. Luo, L. J. Zou, X. H. Chen, G. B. Zhang, and Z. Sun

Phys. Rev. B 92, 184512 – Published 24 November 2015

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Electronic structure in a one-Fe Brillouin zone of the iron pnictide superconductors ${CsFe}_{2} {As}_{2}$ and ${RbFe}_{2} {As}_{2}$