Nonlocal conductance of a Majorana wire near the topological transition

Abstract: We develop a theory of the nonlocal conductance $G_{RL}(V)$ for a disordered Majorana wire tuned near the topological transition critical point. We show that the differential conductance is an odd function of bias, $G_{RL}(V) = -G_{RL}(-V)$. We factorize the conductance into terms describing the contacts between the wire and the normal leads, and the term describing quasiparticle propagation along the wire. Topological transition affects only the latter term. At the critical point, the quasiparticle localization length has a logarithmic singularity at the Fermi level, $l(E) \propto \ln(1 / E)$. This singularity directly manifests in the conductance magnitude, as $\ln |G_{RL}(V) / G_Q| \sim L / l(eV)$ for the wire of length $L \gg l(eV)$. Tuning the wire away from the immediate vicinity of the critical point changes the monotonicity of $l(E)$. This change in monotonicty allows us to define the width of the critical region around the transition point.