Fingerprint of Majorana Zero Modes through Nonlocal Measurements
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Enhanced 2πperiodic Aharonov–Bohm Effect as a Signature of Majorana Zero Modes Probed by Nonlocal Measurements
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 92, 054701 (2023).
The enhancement and robustness of the 2π periodic AharonovBohm effect can serve as a nonlocal probe of Majorana zero modes in topological superconductors that are not restricted by fermion parity.
Electrons on the surface of topological superconductors behave as if they are split into two separate locations, a phenomenon known as fractionalization. This feature distinguishes Majorana fermions, specifically Majorana zero modes (MZMs), which have been studied for potential application in topological quantum computations. However, conventional local measurements, such as the quantization of local conductance, have failed to detect them because such characteristics are smeared by the trivial Andreevbound states arising from inhomogeneous potentials around junctions. The nonlocality of MZMs, which arises from fractionalization, necessitates a new detection method. The two bound states at both ends of a onedimensional topological superconductor retain nonlocal correlations, indicating their origin from a single electron. As this remarkable property is absent in trivial bound states, its detection would provide conclusive evidence of MZMs. However, this requires a floating superconductor that preserves the parity of electrons, which hinders experimental realization.
We highlight the significance of the nonlocality of MZMs (electron fractionalization) in considerably amplifying and strengthening the AharonovBohm (AB) effect, even in grounded superconductors where the parity of electrons is not conserved.
We examined a loopshaped junction system consisting of a onedimensional topological superconductor and metal lead wire, and proposed nonlocal conductance measurements to observe the AB effect caused by a magnetic flux penetrating the loop. In general, Andreev reflection occurs at the interface between a superconductor and metal. When electrons in a metal undergo Andreev reflection repeatedly at both ends of the superconducting wire, the nonlocal conductance oscillates with 2π periodicity as a function of the magnetic flux Φ. Multiple Andreev reflections occur at two different junctions when the bound state energies at the two interfaces are close to each other. However, in the topological phase, the energies of the MZMs at both interfaces match closely. This reflects the aforementioned fractionalization phenomenon, leading to a robust AB effect. Our calculations indicated that in the nontopological phase, the AB effect through trivial bound states was considerably influenced by the parameters of the inhomogeneous potentials at the two interfaces and only occurred in a very narrow range of parameters. However, in the topological phase, the AB effect caused by MZMs was robust in all parameter regions. Unlike other nonlocal correlations such as Majoranamediated teleportation, this phenomenon usually occurs without the restriction of fermion parity. The stability of the AB effect against interface details is crucial for detecting MZMs. MZMs and trivial bound states are more distinguishable in nonlocal correlation measurements than in local conductance measurements. Our study proposes that nonlocal correlation measurements may lead to new developments in the quest for MZMs in topological superconductors.
(written by T .Mizushima on behalf of all authors.)
Enhanced 2πperiodic Aharonov–Bohm Effect as a Signature of Majorana Zero Modes Probed by Nonlocal Measurements
(JPSJ Editors' Choice)
J. Phys. Soc. Jpn. 92, 054701 (2023).
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