Topological insulator nanoribbon Josephson junctions: Evidence for size effects in transport properties
Gunta Kunakova, Ananthu P. Surendran, Domenico Montemurro, Matteo Salvato, Dmitry Golubev, Jana Andzane, Donats Erts, Thilo Bauch, Floriana Lombardi
Abstract
We have used Bi2Se3 nanoribbons, grown by catalyst-free physical vapor deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices, we observe a pronounced reduction of the Josephson critical current density Jc by reducing the width of the junction, which in our case corresponds to the width of the nanoribbon. Because the topological surface states extend over the entire circumference of the nanoribbon, the superconducting transport associated with them is carried by modes on both the top and bottom surfaces of the nanoribbon. We show that the Jc reduction as a function of the nanoribbon width can be accounted for by assuming that only the modes traveling on the top surface contribute to the Josephson transport as we derive by geometrical consideration. This finding is of great relevance for topological quantum circuitry schemes since it indicates that the Josephson current is mainly carried by the topological surface states.