ValleytronicsA New Way to Communicate With Electrons

The electronic band structure in crystalline semiconductors represents a relationship between crystal momentum and energy of the electrons and is often depicted by a series of extremum known as valleys. While the use of charge or spin degree of freedom for carrying information is prevalent in today’s technology, the use of electron’s valley degrees of freedom for encoding and processing information (valleytronics) has remained inaccessible for many decades because of inadequate coupling between external excitation and the valley. The advent of two-dimensional materials such as graphene and transition metal dichalcogenides has opened a new avenue for valleytronics which seeks to use valley degrees of freedom to carry and process information, analogues to spin-based spintronics and charge-based electronics. These materials have unique spin-valley locking, imparting a great ability to control and harness electronic valley degrees of freedom with light, electric, and magnetic fields. Here, we present a viewpoint on the fundamental aspects of valleytronics, emphasising valley contrasting characters of two-dimensional semiconductors.