Helical gap and robust zero modes in ballistic PbTe-Pb nanowires

We report possible signatures of Majorana zero modes in PbTe-Pb hybrid nanowires. At zero magnetic field, the normal-state conductance reveals quantized plateaus indicating ballistic transport. Tuning the device into the tunneling and open regimes, we observe a hard superconducting gap and strong Andreev enhancement, respectively, suggesting a low level of disorder. At finite magnetic fields, robust zero-bias conductance peaks can be observed in a sizable parameter space. We then suppress the superconductivity with an out-of-plane magnetic field and apply another field along the nanowire axis. A re-entrance behavior of conductance can be observed, consistent with the formation of a helical gap. The gap size scales with Zeeman energy, and we estimate a spin-orbit energy of 1.5 meV. The coexistence of helical gap and robust zero modes suggests that PbTe-Pb is a promising Majorana candidate.