Numerical study of PbTe-Pb hybrid nanowires for engineering Majorana zero modes

Abstract

Epitaxial semiconductor-superconductor (SM-SC) hybrid nanowires are potential candidates for implementing Majorana qubits. Recent experimental and theoretical works show that charged impurities in SM remain a major problem in all existing hybrid nanowires, in which the SM is either InAs or InSb while the SC is mainly Al. Here, we theoretically validate the recently proposed PbTe-Pb hybrid nanowire as a potential candidate for Majorana devices. By studying the electrostatic and electronic properties of PbTe nanowires, we demonstrate that the huge dielectric constant of PbTe endows itself a high tolerance of charged impurity and a negligible screening from holes on electrostatic gates; and therefore, we believe PbTe has potential advantages over InAs and InSb nanowires. Moreover, we find that the effective axial Landé g factor and Rashba spin-orbit coupling strength of PbTe nanowires are comparable to those of InAs nanowires. The conceivable merits of using Pb as the SC are: i) Pb has a larger superconducting gap, higher critical temperature, and higher parallel critical magnetic field than those of Al; ii) A superconducting gap comparable with those of InAs-Al and InSb-Al can be induced in PbTe-Pb even by a weak coupling between Pb and PbTe, which simultaneously relieves the adverse renormalization and induced disorder effects on SM from SC; iii) Pb film can be grown on PbTe with a thin buffer CdTe layer in between, solving the lattice mismatch problem as an important source of disorder. In the presence of a parallel magnetic field, we show that the typical BdG energy spectrum and tunneling spectroscopy of PbTe-Pb resemble those of InAs and InSb based hybrid nanowires exposed to a titling magnetic field, as a result of the highly anisotropic Landé g factors of PbTe nanowires. The calculated topological phase diagrams of PbTe-Pb indicate that the multivalley character of PbTe makes it easier than InAs and InSb to access topological superconducting phases. Our results could facilitate the experimental realization of PbTe-Pb hybrid nanowires and inspire further theoretical works.

Observation of Aharonov-Bohm effect in PbTe nanowire networks

“…In this work, we choose a different substrate orientation, CdTe(111), for the PbTe growth. Valley-degeneracy breaking along this (111) direction, which is crucial in the realization of MZMs, has been experimentally demonstrated [25,27] and theoretically verified [30].…”

“…Among all 1D candidates, InSb and InAs nanowires are the mostly studied MZM material systems [11][12][13][14][15][16], with AB effect demonstrated [17][18][19][20][21]. Recently, PbTe [22][23][24][25][26][27] based nanowires [28,29] have been proposed as a new MZM candidate [30]. In this paper, we report the observation of AB effect in PbTe nanowire networks.…”