Coulomb correlation effects in LaFeAsO: An LDA + DMFT(QMC) study
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LECTRONIC PROPERTIES OF SOLIDS
Coulomb Correlation Effects in LaFeAsO: An LDA + DMFT(QMC) Study1 A. O. Shorikova, M. A. Korotina, *, S. V. Streltsova, S. L. Skornyakovb, Dm. M. Korotina, and V. I. Anisimova a
Institute of Metal Physics, Russian Academy of Sciences, Yekaterinburg GSP-170, 620041 Russia b Theoretical Physics and Applied Mathematics Department, Urals State Technical University, Yekaterinburg, 620002 Russia *e-mail: [email protected] Received June 10, 2008
Abstract—Effects of Coulomb correlation on the LaFeAsO electronic structure are investigated by the LDA + DMFT(QMC) method (combination of the local density approximation with the dynamic mean-field theory; impurity solver is a quantum Monte Carlo algorithm). The calculation results show that LaFeAsO is in the regime of intermediate correlation strength with a significant part of the spectral density moved from the Fermi energy to the Hubbard bands and far from the edge of the metal–insulator transition. Correlations affect iron dorbitals differently. The t2g states (xz, yz and x2 – y2 orbitals) have a higher energy due to crystal field splitting and are nearly half-filled. Their spectral functions have a pseudogap with the Fermi level position on the higher subband slope. The lower energy eg set (xy and 3z2 – r2 orbitals) have occupancies significantly larger than 1/2 with typically metallic spectral functions. PACS numbers: 74.25.Jb, 71.27.+a, 71.30.+h DOI: 10.1134/S1063776109010154 1
1. INTRODUCTION
The very recent report of superconductivity with the remarkable Tc of 26 K in LaFeAsO1 – xFx [1] has stimulated an intense experimental and theoretical activity. Calculation of the electron–phonon coupling in this material has shown [2] that it cannot give such a high superconducting transition temperature Tc. That resembles the situation with high-Tc cuprates and raises a question about the strength of the Coulomb correlation effects in this material. Recently, Haule et al. [3] reported results of the LDA + DMFT (the local density approximation combined with the dynamic mean-field theory) calculations of the electron structure of an undoped LaFeAsO compound with the effective impurity model solved by the continuous-time quantum Monte Carlo method. According to [3], this system is in a strongly correlated regime. In the present work, we report results of the LDA + DMFT(QMC) calculations for LaFeAsO with an effective impurity model solved by the standard quantum Monte Carlo method in the Hirsch–Fye algorithm. Our results confirm that correlations indeed have a sizable effect on the electron structure of LaFeAsO. But the system is not at the edge of the metal–insulator transition. While Haule et al. [3] claim that the increase in the Coulomb parameter U from 4.0 to 4.5 eV takes 1 The
article is published in the original.
the system to the insulating state, our calculations show that the solution is still clearly metallic even for U = 5.0 eV. 2. COMPUTATION DETAILS The LDA band structure of LaFeAsO was calculated using the method of tight-b
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