Recent advances in theoretical investigations of sliding ferroelectricity in layered and van der Waals two-dimensional materials

With the growing demand for faster, more efficient, and non-volatile memory technologies, ferroelectric (FE) materials have become integral to modern electronics. Sliding FE, arising from the relative motion of van der Waals bonded layers, is more prevalent in layered and two-dimensional (2D) materials than conventional FE. This review explores theoretically proposed sliding FE materials, discussing its origin in charge transfer and orbital distortion. Replacing layers with molecular systems offers a promising avenue to enhance storage density significantly. The impact of external stimuli, such as strain, pressure, and electric fields, is analyzed alongside laser-induced polarization switching and its association with 'dynamical multiferroicity'. Across-layer sliding FE in multilayer systems arising due to next-to-adjacent neighbor permits sliding electric polarization in single-element multilayer systems, thus increasing the range of materials exhibiting sliding FE. The recently proposed FE switching in moiré superlattices in multilayer systems increases the possibility of utilizing more sliding FE in device applications. The review highlights the dependence of spin textures on FE polarization and layer polarization, which has potential applications in spintronics. The coupling of ferroic orders, such as ferroelasticity and (anti)ferromagnetism, presents multistate switching opportunities and the ability to tune one property by manipulating another. A discussion of general theory underscores the importance of material symmetries, such as mirror, inversion, and rotational symmetries, in determining the existence of sliding FE. BrokenPTsymmetry allows the existence of an altermagnetic phase and anomalous Hall effect and magneto-optic Kerr effect in FE antiferromagnets. Continuum electromechanics and thermodynamic analysis reveal a first-order FE-to-paraelectric phase transition. Despite its low energy switching barrier, the robust nature of sliding FE polarization is attributed to the higher intralayer stiffness of 2D materials.