The invisible Majorana bound state at the helical edge

TL;DR

This paper reveals that a Majorana bound state at a quantum spin Hall interface can exist without producing a zero bias conductance peak, challenging the common paradigm linking Majoranas to conductance signatures.

Contribution

It demonstrates the persistent presence of Majorana bound states at certain interfaces regardless of conductance measurements, highlighting a new aspect of topological states in condensed matter.

Findings

Majorana states exist at the interface between magnetically gapped and superconducting quantum spin Hall systems.

Conductance can be zero or quantized depending on energy and barrier scales.

Transition in conductance resembles topological phase transition in spin-orbit coupled wires.

Abstract

The presence of a Majorana bound state in condensed matter systems is often associated to a zero bias peak in conductance measurements. Here, we analyze a system were this paradigm is violated. A Majorana bound state is always present at the interface between a quantum spin Hall system that is magnetically gapped and a quantum spin Hall system gapped by proximity induced s-wave superconductivity. However, the linear conductance could be either zero or nonzero and quantized depending on the energy and length scales of the barriers. The transition between the two values is reminiscent of the topological phase transition in proximitized spin-orbit coupled quantum wires in the presence of an applied magnetic field. We interpret the behavior of the conductance in terms of scattering states at both zero and non-zero energy.