  The valley degree of freedom of electrons in two-dimensional transition metal
dichalcogenides has been extensively studied by theory, optical and
optoelectronic experiments. However, generation and detection of pure valley
current without relying on optical selection have not yet been demonstrated in
these materials. Here, we report that valley current can be electrically
induced and detected through the valley Hall effect and inverse valley Hall
effect, respectively, in monolayer molybdenum disulfide. Specifically,
long-range valley transport is observed over half a micron distance at room
temperature. Our findings will enable a new generation of electronic devices
utilizing the valley degree of freedom, which can be used for future novel
valleytronic applications.
