Spin-Valley Physics in 2D Materials

 

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.

valley zeeman effect

 

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).