Interlayer Sliding Induced Triferroic Coupling in 2D Bilayer NbSi2N4

Interlayer sliding symmetry breaking presents a powerful technique for achieving intrinsic multiferroic coupling among magnetism, ferroelectricity, and valley polarization, thereby establishing a new paradigm for the design of multifunctional devices. First-principles calculations unveil multiferroic coupling in 2D NbSi2N4. The monolayer exhibits a ferromagnetic ground state, where valley polarization is tuned by magnetic moment reversal. The energetically stable AB/BA-stacked bilayer hosts coexisting triferroic orders: antiferromagnetism, ferrovalley, and out-of-plane ferroelectricity. The interlayer-sliding-induced AB to BA transition enables non-volatile ferroelectric bistability via polarization reversal. The magneto-optic Kerr effect (MOKE) confirms magnetoelectric coupling between sliding ferroelectricity and antiferromagnetism. Valley polarization reversal is achieved by electric-field-driven polarization switching or magnetic-field-controlled magnetization direction flipping, inducing a significant stacking-dependent anomalous valley Hall effect (AVHE) and spin currents. This establishes NbSi2N4 as an ideal platform for novel non-volatile memory and spin-valleytronic devices.