Majorana-Klein hybridization in topological superconductor junctions

We present a powerful and general approach to describe the coupling of Majorana fermions to external leads, of interacting or non-interacting electrons. Our picture has the Klein factors of bosonization appearing as extra Majoranas hybridizing with the physical ones. We demonstrate the power of this approach by solving a highly nontrivial SO(M) Kondo problem arising in topological superconductors with M Majorana-lead couplings, allowing for arbitrary M and for conduction electron interactions. We find that these topological Kondo problems give rise to robust non-Fermi liquid behavior, even for Fermi liquid leads, and to a quantum phase transition between insulating and Kondo regimes when the leads form Luttinger liquids. In particular, for M=4 we find a long sought-after stable realization of the two-channel Kondo fixed point.