  Valleytronics rooted in the valley degree of freedom is of both theoretical
and technological importance as it offers additional opportunities for
information storage and electronic, magnetic and optical switches. In analogy
to ferroelectric materials with spontaneous charge polarization in electronics,
as well as ferromagnetic materials with spontaneous spin polarization in
spintronics, here we introduce a new member of ferroic-family, i.e. a
ferrovalley material with spontaneous valley polarization. Combining a two-band
kp model with first-principles calculations, we show that 2H-VSe2 monolayer,
where the spin-orbit coupling coexists with the intrinsic exchange interaction
of transition-metal-d electrons, is such a room-temperature ferrovalley
material. We further predict that such system could demonstrate many
distinctive properties, for example, chirality-dependent optical band gap and
more interestingly, anomalous valley Hall effect. On account of the latter, a
series of functional devices based on ferrovalley materials, such as
valley-based nonvolatile random access memory, valley filter, are contemplated
for valleytronic applications.
