Orbital-selective Mott transitions in the anisotropic two-band Hubbard model at finite temperatures

The anisotropic degenerate two-orbital Hubbard model is studied within dynamical mean-field theory at low temperatures. High-precision calculations on the basis of a refined quantum Monte Carlo (QMC) method reveal that two distinct orbital-selective Mott transitions occur for a bandwidth ratio of 2, even in the absence of spin-flip contributions to the Hund exchange. The second transition—not seen in earlier studies using QMC, iterative perturbation theory, and exact diagonalization—is clearly exposed in a low-frequency analysis of the self-energy and in local spectra.

Figure 1

(Color online) (b) Ratio $r=Z_{\text{narrow}}∕Z_{\text{wide}}$ of the discrete QMC estimates of the quasiparticle weights of both bands (shown in the inset) vs interaction $U$ for various temperatures $T$; lines for $U>2.1$ represent piecewise quadratic fits. (a) Same data with linear offset.

Figure 2

(Color online) Low-frequency analysis of the self-energy for $T=1∕32$: QMC data (crosses: for $\Delta \tau =0.40$, circles: for $\Delta \tau =0.32$) for the product of frequency $\omega$ and self-energy $\Sigma$ at the Matsubara frequencies is extrapolated by cubic polynomials in $\omega$ for the narrow/wide band (upper/lower panel). Inset: extrapolated value for $\omega \to i{0}^{+}$.

Figure 3

(Color online) Spectral function of narrow/wide band (upper/lower panel) from QMC$+$MEM for $T=1∕40$.

Figure 4

(Color online) QMC estimates for value $N\left(0\right)$ of spectral function at Fermi energy vs interaction. Full/empty symbols correspond to the narrow/wide band at $\Delta \tau =0.4$; crosses to results for $\Delta \tau =0.32$ at $T=1∕32$.

Figure 5

(Color online) Intraorbital double occupancy $D_m=⟨n_{m\uparrow }{n}_{m\downarrow }⟩$. Lines indicate piecewise cubic fits. Upper panel: a linear offset exposes the features of the wide band.