Ferroelectric multi-stability and electrically switchable Rashba effect in few-layer M2CO2 (M = Ti, Zr, Hf)

Abstract

Manipulating the interlayer stacking in van der Waals materials offers a powerful approach for designing emergent quantum devices. Using first-principles calculations, we investigate the layer-dependent ferroelectric and spintronic properties of few-layer M2CO2 (M = Ti, Zr, Hf). In bilayer structures, interlayer sliding breaks the mirror symmetry of the nonpolar parent phase, leading to ferroelectric bistability with a switchable out-of-plane polarization ranging from 1.38 to 4.12 pC/m. In the trilayer configuration, the system exhibits ferroelectric tri-stability, characterized by a stable intermediate nonpolar state flanked by two polar states. This triple-well energy landscape provides a mechanism for ternary data storage. Furthermore, the ferroelectric polarization is coupled to the electronic spin texture, enabling switching between a spin-degenerate state and Rashba-split polar states. These findings establish M2CO2 as a promising candidate material for multi-level memory and nonvolatile spintronic logic devices.