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arXiv 2001.10551cond-mat.mes-hall
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一维半导体-超导体异质结构中 Majorana 与 Andreev 束缚态能量振荡的对比

Majorana versus Andreev bound state energy oscillations in a 1D semiconductor-superconductor heterostructure

Gargee Sharma, Chuanchang Zeng, Tudor D. Stanescu, Sumanta Tewari

AI总结:

研究半导体-超导体异质结构中 Majorana 零模与 Andreev 束缚态的能量振荡差异,通过数值计算证明振幅增大振荡是拓扑 Majorana 零模的通用属性,而振幅减小振荡是平凡 Andreev 束缚态的属性。

摘要:

最近在半导体-超导体 Majorana 纳米线中观察到的能量振荡衰减现象,与基于系统两端存在局域化 Majorana 零模的典型预期形成对比,后者预测混合化能量振荡的振幅会随外加磁场增加而增大。这些观察结果最近通过考虑纳米线末端附近位置依赖的阶跃型自旋轨道耦合得到了理论上的证明,这种耦合可能源于标准隧穿电导实验中隧穿门的存在。在这里,我们表明,与 Majorana 振荡振幅随外加场增大的参数区域相比,发生这种现象的参数空间窗口极其微小。此外,包含位置依赖的有效势(该势也自然地由隧穿门等在导线末端附近诱发),实际上消除了与衰减振荡相关的小窗口。通过广泛的数值计算,我们表明,正如预期的那样,混合化能量的振幅增大振荡代表拓扑 Majorana 零模的通用属性,而振幅减小振荡是通常在非均匀系统中出现的低能平凡 Andreev 束缚态的通用属性。通过对多个现实参数配置进行平均,我们识别出混合化能量的稳健特征,这些特征可以在典型的微分电导实验中观察到,而无需微调控制参数。

英文摘要:

The recent experimental observations of decaying energy oscillations in semiconductor-superconductor Majorana nanowires is in contrast with the typical expectations based on the presence of Majorana zero modes localized at the ends of the system, when the amplitude of the hybridization energy oscillations is predicted to increase with the applied magnetic field. These observations have been theoretically justified recently by considering a position-dependent, step-like spin-orbit coupling near end of the nanowire, which could arise due to the presence of tunnel gates in a standard tunneling conductance experiment. Here, we show that the window in parameter space where this phenomenology occurs is vanishingly small, when compared to the parameter region where Majorana oscillations increase in amplitude with the applied field. Further, including a position-dependent effective potential, which is also induced naturally near the end of the wire by, e.g., tunnel gates, practically removes the small window associated with decaying oscillations. Using extensive numerical calculations, we show that, as expected, increasing amplitude oscillations of the hybridization energy represent a generic property of topological Majorana zero modes, while decreasing amplitude oscillations are a generic property of low-energy trivial Andreev bound states that typically emerge in non-homogeneous systems. By averaging over several realistic parameter configurations, we identify robust features of the hybridization energy that can be observed in a typical differential conductance experiment without fine-tuning the control parameters.

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