Mardi 3 Juillet 2012 salle Remy Lemaire (K223) à 9h30
Superconducting transport in the 3-D topological insulators Bi2Se3 and HgTe
Three-dimensional topological insulators are a newly discovered class of materials characterized by the presence of a bandgap in their bulk and gapless Dirac fermions at their surfaces. Owing to the presence of Dirac fermions, new physical phenomena are predicted to occur. However, isolating the contribution of Dirac fermions in electronic transport has proven to be difficult. I will present our recently published experimental results on transport through gated Josephson junctions fabricated on thin single crystals of the 3-D topological insulator Bi2Se3. At sufficiently high perpendicular magnetic field, we observe the filling of Landau levels of the Dirac fermions, whose character evolves continuously from electron- to hole-like. When the electrodes are in the superconducting state (B=0), we observe a supercurrent through these junctions. More recently, we have performed transport measurements on Josephson junctions based on thick strained HgTe layers, which are also a 3-D topological insulator. The Fermi level resides in the bandgap that originates from the applied in-plane strain. Since the bandgap is almost free of impurity states, transport is mainly through the topological surface states. Here, I will present our results on induced superconductivity and Josephson supercurrent through the Dirac-like surface states of strained HgTe. The demonstration of a Josephson supercurrent through surface states of a 3-D topological insulator is an essential step towards the development of more sophisticated superconducting devices to investigate the appearance of so-called Majorana fermions.