Electronic structure of the iron-based superconductor LaOFeP

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Abstract

The recent discovery of superconductivity in the iron oxypnictide family of compounds1,2,3,4,5,6,7,8,9 has generated intense interest. The layered crystal structure with transition-metal ions in planar square-lattice form and the discovery of spin-density-wave order near 130 K (refs 10, 11) seem to hint at a strong similarity with the copper oxide superconductors. An important current issue is the nature of the ground state of the parent compounds. Two distinct classes of theories, distinguished by the underlying band structure, have been put forward: a local-moment antiferromagnetic ground state in the strong-coupling approach12,13,14,15,16,17, and an itinerant ground state in the weak-coupling approach18,19,20,21,22. The first approach stresses on-site correlations, proximity to a Mott-insulating state and, thus, the resemblance to the high-transition-temperature copper oxides, whereas the second approach emphasizes the itinerant-electron physics and the interplay between the competing ferromagnetic and antiferromagnetic fluctuations. The debate over the two approaches is partly due to the lack of conclusive experimental information on the electronic structures. Here we report angle-resolved photoemission spectroscopy (ARPES) of LaOFeP (superconducting transition temperature, Tc = 5.9 K), the first-reported iron-based superconductor2. Our results favour the itinerant ground state, albeit with band renormalization. In addition, our data reveal important differences between these and copper-based superconductors.

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Figure 1: Comparison between angle-integrated photoemission spectrum and calculated density of states.
Figure 2: Comparison between angle-resolved photoemission spectra and LDA band structures along two high-symmetry lines.
Figure 3: Energy distribution curves along two high-symmetry lines.
Figure 4: Fermi surface maps of LaOFeP.

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Acknowledgements

We thank C. Cox, S. M. Kauzlarich and H. Hope for single-crystal X-ray diffraction measurements, and H. Yao, S. A. Kivelson, R. M. Martin, S. C. Zhang and X. L. Qi for discussions. ARPES experiments were performed at the Advanced Light Source, which is operated by the US Department of Energy Office of Basic Energy Science. Work at Stanford and Oak Ridge National Laboratory was supported by the Office of Basic Energy Science, Division of Materials Science and Engineering.

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Correspondence to D. H. Lu or Z.-X. Shen.

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Supplementary Information

This file contains a summary of the samples, the experimental method, and the band structure calculations used in this paper. (PDF 86 kb)

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Lu, D., Yi, M., Mo, S. et al. Electronic structure of the iron-based superconductor LaOFeP. Nature 455, 81–84 (2008) doi:10.1038/nature07263

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