The Finite Temperature Effect on Josephson Junction between an s-Wave Superconductor and an s_±-Wave Superconductor

We investigate a Josephson junction between a one-band and a multi-band s-wave superconductor. When the multi-band lead is an s_±-wave superconductor, we find that the critical Josephson current may change its sign when the temperature changes. Our result confirms that this is a widespread effect of the s_±-wave superconductor, independent of the type of the junction, the ratios of the gaps and superconducting transition temperatures, as long as the tunneling matrix elements have suitable values. This novel effect comes directly from the opposite gap signs. We propose that the observation of this phenomena can be used to detect the s_±-wave pairing symmetry in iron-based superconductors.