Sliding ferroelectricity of multilayer h-BN.

The emergence of two-dimensional ferroelectrics has spurred significant interest for beyond-Moore electronics. Recent breakthroughs have demonstrated the robust out-of-plane ferroelectricity in specifically engineered hexagonal boron nitride (h-BN) configurations interlayer sliding mechanisms. We systematically investigate stacking-dependent ferroelectric ordering in multilayer h-BN using first principles calculation methods and the modern theory of polarization. In the h-BN of three layers, interlayer slip disrupts the spatial inversion symmetry of the structure, generating switchable out-of-plane dipoles modulated by stacking sequences. Symmetry analysis of trilayer h-BN reveals 36 distinct stacking orders. These are grouped into 4 transformation sets, each containing 9 stackings that are mutually convertible interlayer sliding. Among these, 30 configurations are non-centrosymmetric. This provides more options for exhibiting ferroelectricity than the bilayer system, where only AB/BA stacking configurations possess an electric dipole moment. We systematically calculate the different characteristics of single-layer sliding and double-layer sliding in trilayer h-BN. When the number of layers further increases, we propose two stacking strategies to enhance electric dipole moments: (1) introducing AB stacking for polarization accumulation and (2) employing AA' antiparallel stacking to amplify vertical dipoles. These findings provide fundamental insights into sliding ferroelectric mechanisms in h-BN multilayers and establish design principles for developing ultracompact ferroelectric devices with tailored polarization characteristics.