Research: Charge frustration drives novel insulating states

Frustration in spin systems has been extensively studied, but charge frustration --- the competing tendencies in electron charge configurations --- remains comparatively unexplored. Electronic polarization, which couples mobile charges to induced dipoles, can generate strong charge frustration in a one-dimensional extended Hubbard model. Within this frustrated regime, the analysis uncovers a previously unreported charge-disordered insulating (CDI) phase, which lacks both charge order and magnetic order yet remains insulating. The CDI phase is distinct from a conventional Mott insulator, featuring unusually enhanced local double occupancy. The study also identifies an extremely fragile ferroelectric phase and an exotic eight-site periodic charge-density-wave state stabilized by quantum fluctuations. These findings demonstrate that polarization-driven charge frustration provides a robust pathway to unconventional insulating and charge-ordered phases in low-dimensional correlated systems. The results have implications for a variety of platforms, including organic conductors, transition-metal oxides, and ultracold polar molecules, where such polarization effects may be experimentally realized.

S. Saha, J. van den Brink, M. Kumar, S. Nishimoto,
Polarization-Driven Charge Frustration and Emergent Phases in the One-Dimensional Extended Hubbard Model,
Phys. Rev. Lett. 135, 206504 (2025) (arXiv)