Valley manipulation by external fields in two-dimensional materials and their hybrid systems.

Investigating two-dimensional (2D) valleytronic materials opens a new chapter in physics and facilitates the emergence of pioneering technologies. Nevertheless, this nascent field faces substantial challenges, primarily attributed to the inherent issue of valley energy degeneracy and the manipulation of valley properties. To break these constraints, the application of external fields has become pivotal for both generating and manipulating the valley properties of 2D systems. This paper takes a close look at the latest progress in modulating the valley properties of 2D valleytronic materials using external fields, covering a wide array of configurations from monolayers and bilayers to intricate heterostructures. We hope that this overview will inspire more exciting discoveries and significantly propel the evolution of valleytronics within the realm of 2D material research.