Time-Reversal-Invariant Topological Superconductivity

The discovery of topological band insulators has created a revolution in condensed matter physics. We generalize the essential idea of band inversion and symmetry protection to experimentally feasible superconducting systems with time-reversal symmetry. When such a one-dimensional system becomes topological nontrivial, a Majorana Kramers pair appears on the boundary, producing quantized tunneling conductance plateaus and unprecedented fractional Josephson effects. The latter effects have two significant implications: (i) the existence of a "periodic building" unifying all the free-fermion topological systems and (ii) the possibility of fractionalization in superconductors.