Zero-energy Andreev bound states from quantum dots in proximitized Rashba nanowires

Abstract

We study an analytical model of a Rashba nanowire that is partially covered by and coupled to a thin superconducting layer, where the uncovered region of the nanowire forms a quantum dot. We find that, even if there is no topological superconducting phase possible, there is a trivial Andreev bound state that becomes pinned exponentially close to zero energy as a function of magnetic field strength when the length of the quantum dot is tuned with respect to its spin-orbit length such that a resonance condition of Fabry-Perot type is satisfied. In this case, we find that the Andreev bound state remains pinned near zero energy for Zeeman energies that exceed the characteristic spacing between Andreev bound state levels but that are smaller than the spin-orbit energy of the quantum dot. Importantly, as the pinning of the Andreev bound state depends only on properties of the quantum dot, we conclude that this behavior is unrelated to topological superconductivity.To support our analytical model, we also perform a numerical simulation of a hybrid system while explicitly incorporating a thin superconducting layer, showing that all qualitative features of our analytical model are also present in the numerical results. arXiv:1810.09840v2 [cond-mat.mes-hall]

Majorana fermions in magnetic chains

“…Altogether, these observations lend reasonable support to the existence of MZMs in solid-state systems. At the same time, an alternative explanation that the observed zero-bias peaks in transport measurements could also arise due to topologically trivial Andreev bound states originating within the normal regime has been put forth [93,94,95,96,97,98,99,100].…”

“…Non-Abelian statistics and braiding of MZMs in magnetic chainsAlthough the experimental evidence presents a compelling case for the existence of zero energy bound states at the ends of magnetic chains (see Sec. 4), it has not distinguished the results from other zero energy modes, such as Kondo resonances[92], Andreev states[93,94,95,96,97,98,99,100], or Tamm-Shockley states[101,102]. In order to uniquely identify the end states as MZMs, one needs to consider the effect of exchanging three MZMs to determine if these states indeed obey non-Abelian statistics.…”

Zeeman Tunability of Andreev Bound States in van der Waals Tunnel Barriers

“…13,14 The combination of superconductivity, strong spin-orbit coupling and Zeeman field can form trivial nearly zero energy bound states in quantum dots, as recently shown in refs. 18,19 There, a non superconducting quantum dot, in contact with a BCS superconductor, was theoretically shown to host such bound states when a magnetic field crosses a threshold, determined by the superconducting gap and the strength of the SOC. While the details of the discussed model and our van der Walls system are different, we believe that the phenomenon of pinning to zero bias is general.…”

Influence of long-range interaction on Majorana zero modes

“…Here quantum qubit registers are stored in spatially separated MZMs, which are topologically protected from noise and decoherence [41,42]. The localized Majorana modes can also be manipulated by solely acting on the quantum dots [11,12,[43][44][45][46][47][48]. For practical applications, it is crucial to describe the source of the decoherence in the system.…”