Robust optical emission polarization in MoS <inf>2</inf> monolayers through selective valley excitation

We report polarization resolved photoluminescence from monolayer MoS 2, a two-dimensional, noncentrosymmetric crystal with direct energy gaps at two different valleys in momentum space. The inherent chiral optical selectivity allows exciting one of these valleys, and close to 90% polarized emission at 4 K is observed with 40% polarization remaining at 300 K. The high polarization degree of the emission remains unchanged in transverse magnetic fields up to 9 T indicating robust, selective valley excitation. © 2012 American Physical Society