An Extraordinary Josephson Junction

The combination of symmetry breaking effects, such as those occurring in magnets and superconductors, with topological order may result in remarkable new physics. Recent theoretical studies suggest that, in certain superconductors, exotic quasiparticle excitations can emerge that behave like Majorana fermions, chargeneutral quasiparticles that are their own antiparticles. In Physical Review Letters, Jimmy Williams at Stanford University, California, and colleagues [1] combine the superconducting Josephson effect, which is a profound consequence of symmetry breaking, with topological order in hybrid superconductor-topological insulator structures. The structure investigated by the authors exhibits unconventional behavior that may be related to the emergence of Majorana states. In a Josephson junction, consisting of two superconductors separated by a thin nonsuperconducting barrier, symmetry breaking results in a supercurrent, i.e., a dissipationless current, that depends on the phase difference (φ1 − φ2) across the junction via the current-phase relation