Chalcogenic orbital density waves in weak and strong coupling limit

TL;DR

This paper investigates how Coulomb interactions influence orbital density waves in a one-dimensional p-orbital Hubbard model, revealing different phases in weak and strong coupling regimes and aligning with experimental observations in elemental chalcogens.

Contribution

It introduces a detailed analysis of orbital density wave formation in a helical chain model, highlighting the dependence on interaction strength and identifying a phase transition.

Findings

Orbital density wave with period three emerges in the ground state.

The form of the orbital order varies significantly between weak and strong coupling.

Realistic Coulomb interactions in elemental chalcogens favor the weak coupling phase.

Abstract

Stimulated by recent works highlighting the indispensable role of Coulomb interactions in the formation of helical chains and chiral electronic order in the elemental chalcogens, we explore the p-orbital Hubbard model on a one-dimensional helical chain. By solving it in the Hartree approximation we find a stable ground state with a period-three orbital density wave. We establish that the precise form of the emerging order strongly depends on the Hubbard interaction strength. In the strong coupling limit, the Coulomb interactions support an orbital density wave that is qualitatively different from that in the weak-coupling regime. We identify the phase transition separating these two orbital ordered phases, and show that realistic values for the inter-orbital Coulomb repulsion in elemental chalcogens place them in the weak coupling phase, in agreement with observations of the order in the elemental chalcogens.