A recent addition to low-dimensional materials are monolayer transition metal dichalcogenides (TMDs), such as WSe₂, with an atomically thin, honeycomb lattice and optical band gaps. In addition to spin, charge carriers in TMDs exhibit a “valley” degree of freedom, which behaves like a pseudospin. The two valleys can be optically addressed using circularly polarized light, opening up exciting possibilities for “valleytronics". In addition, in analogy to spin Zeeman effect, a valley Zeeman effect has been observed which allows for a magnetic control of valleys.¹ Another curious aspect of TMDs lies in the non-trivial geometry of their band structure which gives rise to equal but opposite Berry curvature, an effective magnetic field in the momentum space. This together with a large spin-orbit interaction and strong light-matter interactions makes TMDs especially suitable for investigating spin-valley physics.

We combine electrical and optical measurements to investigate coupled spin-valley dynamics in TMDs and their heterostructures. In particular, we are interested in studying the interplay of non-trivial geometry of bands (Berry phase effects), strong Coulomb interactions and strong spin-orbit coupling in TMDs. A goal of this study is to realize quantum control of energy/information and light-enabled topological states of matter.

¹“Valley Zeeman effect in elementary optical excitations of monolayer WSe₂,” A. Srivastava, M. Sidler, A.V. Allain, D. S. Lembke, A. Kis, A. Imamoglu, Nature Phys. 11, 141-147 (2015).