Charge Singlets and Orbital-Selective Charge Density Wave Transitions

Abstract

The possibility of "orbitally selective Mott transitions" within a multiband Hubbard model, in which one orbital with large on-site electron-electron repulsion $U_1$ is insulating and another orbital, to which it is hybridized, with small $U_{-1}$, is metallic, is a problem of long-standing debate and investigation. In this paper we study an analogous phenomenon, the co-existence of metallic and insulating bands in a system of orbitals with different electron-phonon coupling (EPC). To this end, we examine two variants of the bilayer Holstein model: a uniform bilayer and a "Holstein-Metal interface" where the electron-phonon coupling, $\lambda$, is zero in the "metallic" layer. In the uniform bilayer Holstein model, charge density wave (CDW) order dominates at small interlayer hybridization $t_3$, but decreases and eventually vanishes as $t_3$ grows, providing a charge analog of singlet (spin liquid) physics. In the interface case, we show that CDW order penetrates into the metal layer and forms long-range CDW order at intermediate ratio of inter- to intra-layer hopping strengths, $1.4\lesssim t_3/t\lesssim 3.4$. This is consistent with the occurrence of an "orbitally selective CDW" regime at weak $t_3$ in which the layer with ${\lambda }_1\ne 0$ exhibits long-range charge order, but the "metallic layer" with ${\lambda }_{-1}=0$, to which it is hybridized, does not.

10 pages, 11 figures

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• Attractive Su-Schrieffer-Heeger-Hubbard Model on a Square Lattice Away from Half-Filling
• Bose-Einstein condensation in honeycomb dimer magnets and $\mathrm{Y}{\mathrm{b}}_2\mathrm{S}{\mathrm{i}}_2{\mathrm{O}}_7$
• Magnetic, charge, and bond order in the two-dimensional Su-Schrieffer-Heeger-Holstein model
• Enhancement of Charge Density Wave Correlations in a Holstein Model with an Anharmonic Phonon Potential