Theoretical evidence for strong correlations and incoherent metallic state in FeSe

The role of electronic Coulomb correlations in iron-based superconductors is an important open question. We provide theoretical evidence for strong correlation effects in FeSe, based on dynamical mean field calculations. Our ab initio spectral properties first demonstrate the existence of a lower Hubbard band. Moreover, together with significant orbital-dependent mass enhancements, we find that the normal state is a bad metal over an extended temperature range, implying a non-Fermi liquid due to formation of local moments. Predictions for angle-resolved photoemission spectroscopy are made.

Figure 1

(Color online) Comparison of the total LDA DOS (black, thin) to the spectral function obtained with DMFT (red, thick). “LHB” denotes the lower Hubbard band. The inset shows the evolution of the LHB as a function of $U$, with $J$ scaled accordingly ($J=0.9,1.1,1.3$, respectively.)

Figure 2

(Color online) Orbital-resolved comparison of the density of states between the LDA (thin black) and DMFT (thick, red) results. The orbitals in the bottom row show strongest correlations. Note the LHB in the $d_{xy}$ orbital.

Figure 3

Comparison of the momentum-resolved spectral function of DFT (top) to the $\text{DFT}+\text{DMFT}$ results (bottom).

Figure 4

Comparison of the low-energy spectral function, projected to orbital character, of DFT (left) to the $\text{DFT}+\text{DMFT}$ results (right). Top row: $d_{xy}$ orbital. Bottom row: degenerate $d_{xz}$, $d_{yz}$ orbitals.

Figure 5

(Color online) Difference of the total DOS when calculated using the full four-index $U$-matrix (black) and density-density interactions (red). For both calculations: $U=4.06\text{eV}$, $J=0.91\text{eV}$.