Orbital Multiferroicity in Two-Dimensional Triangular Lattice

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Abstract
The search for multiferroicity in two-dimensional (2D) systems has predominantly focused on spin-driven mechanisms, leaving the distinct physics of coupled spin-orbital orders largely unexplored. Here, we propose a theoretical mechanism for orbital multiferroicity on 2D triangular lattices, arising from the intrinsic interplay between ferro-orbital and magnetic orders. Through symmetry analysis and effective model derivation, we reveal that the orbital order imposes a strong interaction on the magnetic sector, activating robust orbiton-magnon hybridization. Using density-functional theory calculations, we substantiate this mechanism in monolayer FeH_{2}, where cooperative orbital and spin interactions stabilize an antiferro-orbital antiferromagnetic ground state. Remarkably, mechanical strain efficiently tunes these interactions, enabling reversible phase transitions between the antiferro-orbital and ferro-orbital states. Crucially, the elementary excitation spectrum exhibits hybridization gaps, serving as a definitive fingerprint of the formed entangled magnon-orbiton modes. Our Letter thus establishes a novel paradigm for exploring orbital multiferroicity in 2D systems.
Funding Information
  • National Natural Science Foundation of China (12274261)
  • Natural Science Foundation of Shandong Province (ZR2024QA016)
  • Shandong Province Fundamental Research Zone (TQ012025003)
  • Shandong Province Fundamental Research Zone (YDZX2025150)

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