Size matters for transport in topological insulator nanoribbons

Read our recent work on topological insulator Bi₂Se₃ nanoribbons.

We have grown Bi₂Se₃ nanoribbons by catalyst-free Physical Vapor Deposition, and employed them to fabricate  high quality Josephson junctions. In these devices we have observed a pronounced size effect in the transport properties: a strong reduction of the Josephson critical current density J_c occurs by reducing the width of the junction, which in our case corresponds to the width of the nanoribbon.

Since the topological surface states extend over the entire circumference of the nanoribbon, the superconducting transport associated  to  these states  is  carried  by  modes  on  both  the  top  and  bottom  surfaces  of  the nanoribbon.   The J_c reduction as a function of the nanoribbons width shows that only the modes traveling on the top surface contribute  to  the  Josephson  transport. The reduction qualitatively agrees with the calculation of the top surface modes by using geometrical  considerations. 

This finding, recently published on Journal of Applied Physics (link), is of a great relevance for topological quantum circuitry schemes, since it indicates that the Josephson current is mainly carried by the topological surface states. The work has been done in collaboration with the University of Latvia.