  The Josephson rectification effect, where the resistance is finite in one
direction while zero in the other, has been recently realized experimentally.
The resulting Josephson diode has many potential applications on
superconducting devices, including quantum computers. Here, we theoretically
show that a superconductor-normal metal-superconductor Josephson junction diode
on the two-dimensional surface of a topological insulator has large tunability.
The magnitude and sign of the diode quality factor strongly depend on the
external magnetic field, gate voltage, and the length of the junction. Such
rich properties stem from the interplay between different current-phase
relations for the multiple transverse transport channels, and can be used for
designing realistic superconducting diode devices.
