Protected gap closing in Josephson trijunctions constructed on Bi2Te3

We carried out a phase-sensitive experiment on Josephson trijunctions constructed on the surface of three-dimensional topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. Through local flux contol and contact resistance measurement, we observed that the minigap at the ends of the trijunctions approaches zero linearly with varying phase difference and closes completely at $\ensuremath{\pi}$ phase difference. The minigap at the center of the trijunction is protected to close over extended regions in phase space. These results agree with the theory by Fu and Kane [Phys. Rev. Lett. 100, 096407 (2008)].