Majorana/Andreev crossover and the fate of the topological phase transition in inhomogeneous nanowires
Majorana/Andreev crossover and the fate of the topological phase transition in inhomogeneous nanowires
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DOI：
10.1088/1361-648x/ac44d2
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发表时间：
2021-12
期刊：
影响因子：
--
通讯作者：
P. Marra;A. Nigro
中科院分区：
文献类型：
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作者：
P. Marra;A. Nigro
在实际的马约拉纳纳米线装置中，马约拉纳束缚态（MBS）和安德烈耶夫束缚态（ABS）具有相似的实验特征，这使得它们很难相互区分。在此，我们根据全局和局部拓扑不变量、费米子宇称、准粒子密度、马约拉纳赝自旋和自旋极化、密度重叠以及相反马约拉纳分量之间的跃迁概率，描述了在完全分离、部分分离和完全重叠的马约拉纳模式之间插值的连续马约拉纳/安德烈耶夫交叉情况。我们发现，在非均匀纳米线中，完全重叠的平凡安德烈耶夫束缚态和非平凡马约拉纳束缚态之间的转变不一定要求准粒子激发的体隙关闭，而是部分分离的马约拉纳模式（ps - MM）从平凡态到非平凡态的简单宇称交叉。我们证明，完全分离和完全重叠的马约拉纳模式对应于连续交叉相反两侧的两种极限情况：两者之间的唯一区别可以通过估计马约拉纳分量的分离程度来获得。这一结果与体 - 边对应并不矛盾：实际上，驱动马约拉纳/安德烈耶夫交叉的场不均匀性具有与纳米线长度相当的长度尺度，因此对应于一种破坏马约拉纳束缚态拓扑保护的非局域扰动。
Majorana bound states (MBS) and Andreev bound states (ABS) in realistic Majorana nanowires setups have similar experimental signatures which make them hard to distinguishing one from the other. Here, we characterize the continuous Majorana/Andreev crossover interpolating between fully-separated, partially-separated, and fully-overlapping Majorana modes, in terms of global and local topological invariants, fermion parity, quasiparticle densities, Majorana pseudospin and spin polarizations, density overlaps and transition probabilities between opposite Majorana components. We found that in inhomogeneous wires, the transition between fully-overlapping trivial ABS and nontrivial MBS does not necessarily mandate the closing of the bulk gap of quasiparticle excitations, but a simple parity crossing of partially-separated Majorana modes (ps-MM) from trivial to nontrivial regimes. We demonstrate that fully-separated and fully-overlapping Majorana modes correspond to the two limiting cases at the opposite sides of a continuous crossover: the only distinction between the two can be obtained by estimating the degree of separations of the Majorana components. This result does not contradict the bulk-edge correspondence: indeed, the field inhomogeneities driving the Majorana/Andreev crossover have a length scale comparable with the nanowire length, and therefore correspond to a nonlocal perturbation which breaks the topological protection of the MBS.