Engineering symmetry breaking in 2D layered materials

Symmetry breaking in 2D layered materials plays a significant role in their macroscopic electrical, optical, magnetic and topological properties, including, but not limited to, spin-polarization effects, valley-contrasting physics, nonlinear Hall effects, nematic order, ferroelectricity, Bose–Einstein condensation and unconventional superconductivity. Engineering symmetry breaking of 2D layered materials not only offers extraordinary opportunities to tune their physical properties but also provides unprecedented possibilities to introduce completely new physics and technological innovations in electronics, photonics and optoelectronics. Indeed, over the past 15 years, a wide variety of physical, structural and chemical approaches have been developed to engineer the symmetry breaking of 2D layered materials. In this Technical Review, we focus on the recent progress on engineering the breaking of inversion, rotational, time-reversal and gauge symmetries in 2D layered materials, and present our perspectives on how these may lead to new physics and applications.