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Observation of universal strong orbital-dependent correlation effects in iron chalcogenides.

Yi M, Liu ZK, Zhang Y, Yu R, Zhu JX, Lee JJ, Moore RG, Schmitt FT, Li W, Riggs SC, Chu JH, Lv B, Hu J, Hashimoto M, Mo SK, Hussain Z, Mao ZQ, Chu CW, Fisher IR, Si Q, Shen ZX, Lu DH - Nat Commun (2015)

Bottom Line: Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe0.56Se0.44, monolayer FeSe grown on SrTiO3 and K0.76Fe1.72Se2.We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi surface topologies.Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant.

View Article: PubMed Central - PubMed

Affiliation: 1] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA [2] Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.

ABSTRACT
Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide superconductors. Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe0.56Se0.44, monolayer FeSe grown on SrTiO3 and K0.76Fe1.72Se2. We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi surface topologies. Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant. These observations establish that iron chalcogenides display universal orbital-selective strong correlations that are insensitive to the Fermi surface topology, and are close to an orbital-selective Mott phase, hence placing strong constraints for theoretical understanding of iron-based superconductors.

No MeSH data available.


Related in: MedlinePlus

Quantitative analysis of temperature evolution in the iron chalcogenides.(a–c) Raw spectral images of FTS, FS/STO and KFS taken in the low-temperature state. Yellow regions mark the momentum ranges integrated for energy distribution curve (EDC) analysis for each compound. (d) Integrated EDCs in the yellow region of a for FTS at selected temperatures, fitted by a Shirley background (grey), a Gaussian for the dxy band (blue), and a Gaussian for the dyz band (green), convolved by the Fermi–Dirac function. (e) Integrated EDCs in the yellow region of b for FS/STO at selected temperatures, with a Gaussian background (grey), a Gaussian for the dxy band (blue) and a Gaussian for the dyz band (green). (f) Integrated EDCs in the yellow region of c for KFS at selected temperatures, fitted by a Gaussian background (grey), and a Gaussian for the dxy band (blue). Residual spectral weight for the dxy peak is shaded for each temperature for all compounds. Fitted peaks for the lowest temperature are shown for each compound. (g–i) Temperature dependence of the fitted areas of the dxy and dyz peaks for FTS, FS/STO and KFS. Guides to eye are drawn in grey to show the trends. All curves are normalized by the initial value of the peak area. The error bars in g–i are error bars resulted from the fitting.
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f5: Quantitative analysis of temperature evolution in the iron chalcogenides.(a–c) Raw spectral images of FTS, FS/STO and KFS taken in the low-temperature state. Yellow regions mark the momentum ranges integrated for energy distribution curve (EDC) analysis for each compound. (d) Integrated EDCs in the yellow region of a for FTS at selected temperatures, fitted by a Shirley background (grey), a Gaussian for the dxy band (blue), and a Gaussian for the dyz band (green), convolved by the Fermi–Dirac function. (e) Integrated EDCs in the yellow region of b for FS/STO at selected temperatures, with a Gaussian background (grey), a Gaussian for the dxy band (blue) and a Gaussian for the dyz band (green). (f) Integrated EDCs in the yellow region of c for KFS at selected temperatures, fitted by a Gaussian background (grey), and a Gaussian for the dxy band (blue). Residual spectral weight for the dxy peak is shaded for each temperature for all compounds. Fitted peaks for the lowest temperature are shown for each compound. (g–i) Temperature dependence of the fitted areas of the dxy and dyz peaks for FTS, FS/STO and KFS. Guides to eye are drawn in grey to show the trends. All curves are normalized by the initial value of the peak area. The error bars in g–i are error bars resulted from the fitting.

Mentions: To examine this temperature dependence more carefully, we have quantitatively analysed the spectral weight of each FeCh system. For FTS, we track the dxy hole band slightly away from the Γ point where it is well separated from the dyz hole band (Fig. 5a). From the energy distribution curve at this momentum, we fit Gaussian peaks for both dxy hole band near EF and dyz hole band at higher energies, along with a Shirley background (Fig. 5d), and track the integrated spectral weight of the dxy and dyz peaks as a function of temperature. Comparing these two orbitals, we see that the dxy spectral weight drops to zero ∼110 K, in contrast to a very weak decrease of the dyz spectral weight. This is very similar to the situation in FS/STO and KFS, where we track the spectral weight of the dxy orbital at the dxy electron band bottom at M. For KFS, the fitted peak area precipitously drops ∼100 K, and approaches zero above 180 K (Fig. 5i). For FS/STO, the dxy spectral weight approaches zero above 150 K while that of the dyz orbital remains finite (Fig. 5h), demonstrating the orbital dependence of this temperature evolution.


Observation of universal strong orbital-dependent correlation effects in iron chalcogenides.

Yi M, Liu ZK, Zhang Y, Yu R, Zhu JX, Lee JJ, Moore RG, Schmitt FT, Li W, Riggs SC, Chu JH, Lv B, Hu J, Hashimoto M, Mo SK, Hussain Z, Mao ZQ, Chu CW, Fisher IR, Si Q, Shen ZX, Lu DH - Nat Commun (2015)

Quantitative analysis of temperature evolution in the iron chalcogenides.(a–c) Raw spectral images of FTS, FS/STO and KFS taken in the low-temperature state. Yellow regions mark the momentum ranges integrated for energy distribution curve (EDC) analysis for each compound. (d) Integrated EDCs in the yellow region of a for FTS at selected temperatures, fitted by a Shirley background (grey), a Gaussian for the dxy band (blue), and a Gaussian for the dyz band (green), convolved by the Fermi–Dirac function. (e) Integrated EDCs in the yellow region of b for FS/STO at selected temperatures, with a Gaussian background (grey), a Gaussian for the dxy band (blue) and a Gaussian for the dyz band (green). (f) Integrated EDCs in the yellow region of c for KFS at selected temperatures, fitted by a Gaussian background (grey), and a Gaussian for the dxy band (blue). Residual spectral weight for the dxy peak is shaded for each temperature for all compounds. Fitted peaks for the lowest temperature are shown for each compound. (g–i) Temperature dependence of the fitted areas of the dxy and dyz peaks for FTS, FS/STO and KFS. Guides to eye are drawn in grey to show the trends. All curves are normalized by the initial value of the peak area. The error bars in g–i are error bars resulted from the fitting.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525196&req=5

f5: Quantitative analysis of temperature evolution in the iron chalcogenides.(a–c) Raw spectral images of FTS, FS/STO and KFS taken in the low-temperature state. Yellow regions mark the momentum ranges integrated for energy distribution curve (EDC) analysis for each compound. (d) Integrated EDCs in the yellow region of a for FTS at selected temperatures, fitted by a Shirley background (grey), a Gaussian for the dxy band (blue), and a Gaussian for the dyz band (green), convolved by the Fermi–Dirac function. (e) Integrated EDCs in the yellow region of b for FS/STO at selected temperatures, with a Gaussian background (grey), a Gaussian for the dxy band (blue) and a Gaussian for the dyz band (green). (f) Integrated EDCs in the yellow region of c for KFS at selected temperatures, fitted by a Gaussian background (grey), and a Gaussian for the dxy band (blue). Residual spectral weight for the dxy peak is shaded for each temperature for all compounds. Fitted peaks for the lowest temperature are shown for each compound. (g–i) Temperature dependence of the fitted areas of the dxy and dyz peaks for FTS, FS/STO and KFS. Guides to eye are drawn in grey to show the trends. All curves are normalized by the initial value of the peak area. The error bars in g–i are error bars resulted from the fitting.
Mentions: To examine this temperature dependence more carefully, we have quantitatively analysed the spectral weight of each FeCh system. For FTS, we track the dxy hole band slightly away from the Γ point where it is well separated from the dyz hole band (Fig. 5a). From the energy distribution curve at this momentum, we fit Gaussian peaks for both dxy hole band near EF and dyz hole band at higher energies, along with a Shirley background (Fig. 5d), and track the integrated spectral weight of the dxy and dyz peaks as a function of temperature. Comparing these two orbitals, we see that the dxy spectral weight drops to zero ∼110 K, in contrast to a very weak decrease of the dyz spectral weight. This is very similar to the situation in FS/STO and KFS, where we track the spectral weight of the dxy orbital at the dxy electron band bottom at M. For KFS, the fitted peak area precipitously drops ∼100 K, and approaches zero above 180 K (Fig. 5i). For FS/STO, the dxy spectral weight approaches zero above 150 K while that of the dyz orbital remains finite (Fig. 5h), demonstrating the orbital dependence of this temperature evolution.

Bottom Line: Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe0.56Se0.44, monolayer FeSe grown on SrTiO3 and K0.76Fe1.72Se2.We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi surface topologies.Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant.

View Article: PubMed Central - PubMed

Affiliation: 1] Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, California 94025, USA [2] Departments of Physics and Applied Physics, and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA.

ABSTRACT
Establishing the appropriate theoretical framework for unconventional superconductivity in the iron-based materials requires correct understanding of both the electron correlation strength and the role of Fermi surfaces. This fundamental issue becomes especially relevant with the discovery of the iron chalcogenide superconductors. Here, we use angle-resolved photoemission spectroscopy to measure three representative iron chalcogenides, FeTe0.56Se0.44, monolayer FeSe grown on SrTiO3 and K0.76Fe1.72Se2. We show that these superconductors are all strongly correlated, with an orbital-selective strong renormalization in the dxy bands despite having drastically different Fermi surface topologies. Furthermore, raising temperature brings all three compounds from a metallic state to a phase where the dxy orbital loses all spectral weight while other orbitals remain itinerant. These observations establish that iron chalcogenides display universal orbital-selective strong correlations that are insensitive to the Fermi surface topology, and are close to an orbital-selective Mott phase, hence placing strong constraints for theoretical understanding of iron-based superconductors.

No MeSH data available.


Related in: MedlinePlus