Enhanced altermagnetic splitting through modulating altermagnetic-ferroelectric coupling in monolayer multiferroic Ti2S2O

Two-dimensional (2D) multiferroics hold significant potential for applications in nonvolatile devices due to their small size and low power consumption. However, practical multiferroics are extremely rare due to lack of mechanism that can simultaneously induce strong ferroelectric (FE) polarization and magneto-electric coupling. Here, we report a multiferroic monolayer Ti2S2O exhibiting ultra-strong coupling between altermagnetic (AM) and FE orderings based on first-principles calculations combined with tight-binding model analysis. Through biaxial compressive strain, the FE polarization of monolayer Ti2S2O is enhanced from 0.82 to 1.56 μC/cm2, and the AM splitting is increased from 0.07 to 0.43 eV. Moreover, the tight-binding model is constructed. Accordingly, the observed increase in AM splitting is attributed to enhanced anisotropic second-neighboring hopping between Ti-3dxy orbitals and the nearest-neighboring hopping between Ti-3dxy and S-3p orbitals mediated by strain-tunable FE distortions of non-magnetic O atoms. Our theoretical findings shed light on magneto-electric phenomena and the development of electrically controllable spintronic devices.