Electronic structure of ${\mathrm{YFe}}_{2}{\mathrm{Ge}}_{2}$ studied by angle-resolved photoemission spectroscopy

Electronic structure of ${YFe}_{2} {Ge}_{2}$ studied by angle-resolved photoemission spectroscopy

D. F. Xu, D. W. Shen, D. Zhu, J. Jiang, B. P. Xie, Q. S. Wang, B. Y. Pan, P. Dudin, T. K. Kim, M. Hoesch, J. Zhao, X. G. Wan, and D. L. Feng

Phys. Rev. B 93, 024506 – Published 11 January 2016

Abstract

We report an angle-resolved photoemission spectroscopy study of a ${ThCr}_{2} {Si}_{2}$ -type superconductor ${YFe}_{2} {Ge}_{2}$ ( $T_{c} \approx 1.8$ K) in the normal state. The resolved low-energy band structure mainly consists of several flat Fe bands, while the renormalization factors of different bands range from 1.7 to 2.8. Around the Fermi level, these bands contribute to a high density of states, which may account for the unusually high Sommerfeld coefficient $γ$ . Besides, a 30 meV kink is observed, which is probably induced by electron-phonon interactions. Our results indicate that ${YFe}_{2} {Ge}_{2}$ is a moderately correlated compound, while electron-phonon coupling should be taken into account to better understand its properties.

Received 29 August 2015
Revised 17 December 2015

DOI:https://doi.org/10.1103/PhysRevB.93.024506

Authors & Affiliations

D. F. Xu^1,2,3, D. W. Shen^4,5,*, D. Zhu⁶, J. Jiang^1,2,3, B. P. Xie^1,2,3, Q. S. Wang¹, B. Y. Pan¹, P. Dudin⁷, T. K. Kim⁷, M. Hoesch⁷, J. Zhao^1,3, X. G. Wan⁶, and D. L. Feng^1,2,3,†

¹State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai 200433, China
²Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
³Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433, China
⁴State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050, China
⁵CAS-Shanghai Science Research Center, Shanghai 201203, China
⁶National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, and College of Physics, Nanjing University, Nanjing 210093, China
⁷Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, United Kingdom

^*dwshen@mail.sim.ac.cn
^†dlfeng@fudan.edu.cn

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Vol. 93, Iss. 2 — 1 January 2016

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Figure 1
The crystallographic and transport properties of ${YFe}_{2} {Ge}_{2}$ . (a) Representative unit cell of ${YFe}_{2} {Ge}_{2}$ . (b) The x-ray diffraction pattern of the single crystal. The full width at half maximum (FWHM) of the (008) peak in the rocking scan is about $0 . 074^{\circ}$ . (c) The temperature dependence of the electrical resistivity of the single crystal (from 2.5 to 300 K). Resistivity data for powder at even lower temperatures are shown in the inset, showing a superconducting transition at 1.8 K. (d) The specific heat data of ${YFe}_{2} {Ge}_{2}$ divided by temperature vs temperature squared. The Sommerfeld coefficient is obtained by fitting the data at low temperatures, which are shown in the inset.
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Figure 2
(a) The three-dimensional BZ of ${YFe}_{2} {Ge}_{2}$ . The dashed lines represent the two-dimensional plot of the simplified BZ. (b) Photon-energy-dependent EDCs recorded at normal emission. (c) The photoemission intensity map integrated over $[E_{F} - 5$ meV, $E_{F} + 5$ meV], which is taken with circularly polarized 104 eV photons (around the $Z$ point). The open circles are Fermi crossings determined by the corresponding MDCs. The dashed lines are guides to the eye for the Fermi surface contours. Data were taken at 7 K.
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Figure 3
The photoemission data taken around the $Z$ point. (a) The photoemission intensity plot taken with 101 eV circularly polarized photons along the $Z - A$ direction. (b) The corresponding EDCs for the data in (a). (c) The corresponding MDCs for the data in (a). (d)–(f) The same as those in (a)–(c), but taken along the $Z - R$ direction. Dashed lines are guides for the eye for band dispersions. Data were taken at 7 K.
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Figure 4
The photoemission data taken around the $Γ$ point. (a) The photoemission intensity plot taken with 80 eV circularly polarized photons along the $Γ - M$ direction. (b) The corresponding EDCs for the data in (a). (c) The corresponding MDCs for the data in (a). (d)–(f) The same as those in (a)–(c), but taken along the $Γ - X$ direction. Dashed lines are guides for the eye for band dispersions. Data were taken at 7 K.
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Figure 5
The three-dimensional band structure of ${YFe}_{2} {Ge}_{2}$ . (a) The photon-energy dependence of the MDCs integrated over $[E_{F} - 5$ meV, $E_{F} + 5$ meV] along $Γ (Z) - X (R)$ . (b) The photon-energy dependence of the EDCs at $M (A)$ . (c) The band calculations along high-symmetry directions, showing the highly three-dimensional nature of the band structure. (d) The corresponding band structure along high-symmetry directions. Along $X Γ M$ , solid lines are guides to the eye for the band dispersions. Along $R Z A$ , the calculated band dispersions are renormalized by a factor of 2.5 and overlaid on the photoemission intensity plot for comparison.
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Figure 6
The analysis of the kink. (a) The magnified photoemission intensity plot around the kink taken with circularly polarized 101, 89, and 80 eV photons, respectively. (b) The dispersion of the $δ$ band (89 eV) obtained by fitting the corresponding MDCs. The red dashed line is obtained by fitting the high-energy dispersion linearly. The blue thick line roughly indicates the mode energy. (c), (d) The self-energy analysis of the kink structure.
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Physical Review B

covering condensed matter and materials physics

Electronic structure of ${YFe}_{2} {Ge}_{2}$ studied by angle-resolved photoemission spectroscopy

D. F. Xu, D. W. Shen, D. Zhu, J. Jiang, B. P. Xie, Q. S. Wang, B. Y. Pan, P. Dudin, T. K. Kim, M. Hoesch, J. Zhao, X. G. Wan, and D. L. Feng

Phys. Rev. B 93, 024506 – Published 11 January 2016

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Physical Review B

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Electronic structure of YFe2Ge2 studied by angle-resolved photoemission spectroscopy

D. F. Xu, D. W. Shen, D. Zhu, J. Jiang, B. P. Xie, Q. S. Wang, B. Y. Pan, P. Dudin, T. K. Kim, M. Hoesch, J. Zhao, X. G. Wan, and D. L. Feng

Phys. Rev. B 93, 024506 – Published 11 January 2016

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Electronic structure of ${YFe}_{2} {Ge}_{2}$ studied by angle-resolved photoemission spectroscopy