  We propose a Josephson junction setup based on a topological insulator (TI)
thin film to detect Majorana states, which exploits the unique helical and
extended nature of the TI surface state. When the magnetic flux through the
junction is close to an integer number of flux quanta, Majorana states, present
on both surfaces of the film, give rise to a narrow peak-dip structure in the
current- phase relation by hybridizing at the edge of the junction. Moreover,
the maximal Majorana-state contribution to Josephson current takes a (nearly)
universal value, approximately equal to the supercurrent capacity of a single
quantum-channel. These features provide a characteristic signature of Majorana
states based entirely on supercurrent.
