Valleytronics in 2D semiconductors

In crystalline systems, the electronic band structure determines the relationship between the crystal momentum and energy of an electron. In intrinsic semiconductors, the Fermi energy lies between two bands, where typically the highest valence band below the Fermi energy and lowest conduction band above the Fermi energy determine the electronic and optical physics. These extrema are referred to as crystal momentum space “valleys,” which are stable points in the band structure that electrons or holes can occupy. So that in addition to charge and spin, electrons in a crystalline solid also have a valley degree of freedom that determines the electron’s position in crystal momentum space. The field of valleytronics seeks to use the electron’s valley degree of freedom to encode and process information, analogous to charge in electronics or spin in spintronics. In this chapter, I will review the recent progress in 2D semiconductor valleytronics.