Cartoon graphene/BN device

Topo2D - Topological spin and valley currents

Contacts: Rebeca RIBEIRO-PALAU

The understanding of matter in its deepest form is one of the most fundamental issues of solid state physics. Different states of matter are found to be distinguished by their internal structure, called orders. There exists a special kind of orders, called topological orders, which are universal, meaning that they are robust to arbitrary perturbations. The most common example of this is the quantum Hall effect (QHE), where the topology of the Landau levels leads to the formation of edge states that circulate along the edges of a two-dimensional electron gas. In the edge states, the backscattering between carriers is highly suppressed and therefore, within the channels, charge carriers can be transported without dissipation. The insensitivity of the Hall quantization to fabrication-dependent details and defects is a consequence of the topological properties of the band structure. The QHE is so robust against arbitrary perturbation that is globaly used as the resistance standard of the international SI (systeme international d'unites). 

Additionally to the QHE, there are multiple topologically protected states in nature (e.g., quantum spin Hall effect, topological insulators, topological conductors) which need to be understood and of which this group focus its attention on. To investigate these states the team TOPO2D uses van der Waals heterostructures, in these we combin innovative sample fabrication techniques with new layer alingment control and electron transport measurements at low temperatures.