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Nearly quantized conductance plateau of vortex zero mode in an iron-based superconductor

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Science  10 Jan 2020:
Vol. 367, Issue 6474, pp. 189-192
DOI: 10.1126/science.aax0274

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Reaching a conductance plateau

The surface of the iron-based superconductor FeTe0.55Se0.45 satisfies the necessary conditions to support topological superconductivity. Under the application of a magnetic field, vortices with zero-bias peaks that are consistent with Majorana bound states have been observed. Using scanning tunneling spectroscopy, Zhu et al. studied the conductance of these states as the tip-sample distance was reduced (see the Perspective by Sau). The researchers found that the value of the conductance increased and eventually saturated. For one of the vortices they studied, the conductance reached a quantized value that is characteristic of the Majorana bound states.

Science, this issue p. 189; see also p. 145

Abstract

Majorana zero modes (MZMs) are spatially localized, zero-energy fractional quasiparticles with non-Abelian braiding statistics that hold promise for topological quantum computing. Owing to the particle-antiparticle equivalence, MZMs exhibit quantized conductance at low temperature. By using variable-tunnel–coupled scanning tunneling spectroscopy, we studied tunneling conductance of vortex bound states on FeTe0.55Se0.45 superconductors. We report observations of conductance plateaus as a function of tunnel coupling for zero-energy vortex bound states with values close to or even reaching the 2e2/h quantum conductance (where e is the electron charge and h is Planck’s constant). By contrast, no plateaus were observed on either finite energy vortex bound states or in the continuum of electronic states outside the superconducting gap. This behavior of the zero-mode conductance supports the existence of MZMs in FeTe0.55Se0.45.

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