Correlation-induced spin freezing transition in FeSe: A dynamical mean field study

The effect of local Coulomb interactions on the electronic properties of FeSe is explored within dynamical mean field theory combined with finite-temperature exact diagonalization. The low-energy scattering rate is shown to exhibit non-Fermi-liquid behavior caused by the formation of local moments. Fermi-liquid properties are restored at large electron doping. In contrast, FeAsLaO is shown to be located on the Fermi-liquid side of this spin freezing transition.

Figure 1

(Color online) Orbital average of (a) imaginary part of $3d$ self-energy and (b) spin-spin correlation function for FeSe at various occupancies. For $n>6.3,\dots ,6.5$, the self-energy exhibits FL behavior and the spin susceptibility is Pauli type. At smaller occupancy, the self-energy reveals NFL behavior and the susceptibility becomes Curie-Weiss type, giving rise to bad metallicity caused by spin freezing $\left(T=0.01\text{eV}\right)$.

Figure 2

(Color online) (a) Low-energy scattering rates ${\gamma }_m=-\text{Im}{\Sigma }_m\left(i{\omega }_n\to 0\right)$ and (b) long-time limit of orbital-dependent spin-spin correlations $C_m\left(\tau =\beta /2\right)$ of FeSe as functions of $3d$ occupancy. Near $n=6$, the bad-metallic behavior of ${\gamma }_m>0$ is caused by the formation of local moments. Increasing electron doping restores Fermi-liquid properties whereas hole doping enhances bad-metallic properties.

Figure 3

(Color online) $\text{Fe}3d$ orbital occupancies as functions of chemical potential. $n_{av}$ denotes the average occupancy. Nominal occupancy $n=6$ is reached near $\mu =17\text{eV}$ while at $\mu =15\text{eV}$ all bands are approximately half filled.

Figure 4

(Color online) Low-energy scattering rates and spin-spin correlations derived within ED/DMFT for a degenerate five-band model with Bethe lattice density of states with $W=4\text{eV}$. For $U=4\text{eV}$, $J=0.75\text{eV}$, the spin freezing transition occurs at $n=6.2$ with Fermi-liquid behavior at $n>6.2$ and increasing bad metallicity for $n<6.2$. For $U=4\text{eV}$, $J=0.5\text{eV}$ (not shown), the transition occurs at $n=6.1$.

Figure 5

(Color online) Orbital average of (a) imaginary part of $3d$ self-energy and (b) spin-spin correlation function for FeAsLaO at various occupancies. The Fermi-liquid to non-Fermi-liquid transition caused by local-moment formation occurs close to $n=6$.

Figure 6

(Color online) (a) Low-energy scattering rates and (b) spin-spin correlations of FeAsLaO as functions of $3d$ occupancy. The Fermi-liquid to non-Fermi-liquid transition caused by local-moment formation occurs close to $n=6$. Electron doping maintains Fermi-liquid properties while hole doping leads to bad-metallic behavior.

Figure 7

(Color online) Schematic phase diagram for FeSe and LaFeAsO. Solid curve: spin freezing transition indicating the boundary between Fermi-liquid and non-Fermi-liquid phases. Vertical bar at half filling: Mott insulating phase.