Orbital-Selective Mott Transition out of Band Degeneracy Lifting

We outline a general mechanism for orbital-selective Mott transition, the coexistence of both itinerant and localized conduction electrons, and show how it can take place in a wide range of realistic situations, even for bands of identical width and correlation, provided a crystal field splits the energy levels in manifolds with different degeneracies and the exchange coupling is large enough to reduce orbital fluctuations. The mechanism relies on the different kinetic energy in manifolds with different degeneracy. This phase has Curie-Weiss susceptibility and non-Fermi-liquid behavior, which disappear at a critical doping, all of which is reminiscent of the physics of the pnictides.

Figure 1

Phase diagram for fixed populations $n_m=(1,1.5,1.5)$ (obtained by adjusting the crystal field $\Delta$) within Slave-spin mean-field. Inset: phase diagram for fixed total filling $n=4$ as a function of $U$ and $\Delta$ at $J/U=0.25$. Dashed lines: modification of this diagram under a small splitting ($\sim 0.4/D$) of the two degenerate bands.

Figure 2

Quasiparticle residue as a function of the interaction strength for $J/U=0.25$ and fixed populations $n=(1,1.5,1.5)$ in DMFT with $N_s=9$. Inset: interorbital correlations (top panel) and local spin susceptibility (bottom panel). The cutoff “temperature” (see text) is $\beta D=80$.

Figure 3

Upper panel: local spectral densities for the lifted (solid blue) and the degenerate (dashed red) bands in the Orbital-selective Mott phase. (calculations in DMFT-ED with $N_s=12$ for $U/D=4.5$). Bottom panels: self-energies, respectively, in the metallic ($U/D=1.0$—left) and orbitally selective ($U/D=2.4$—right) phases.

Figure 4

Sketch of the general phase diagram of a doped OSMP. Inset: quasiparticle residues as a function of the filling in SSMF for $U=5$, $J/U=0.25$ and $\Delta =1.5$. The OSMP turns into a Fermi liquid at a finite doping.