Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors
Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors
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DOI：
10.1103/physrevb.101.020504
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发表时间：
2020-01-13
影响因子：
3.7
通讯作者：
Ghaemi, Pouyan
中科院分区：
文献类型：
--
作者：
Ghazaryan, Areg;Lopes, P. L. S.;Ghaemi, Pouyan
在FeTe（1-x）Sex的超导体系中，存在两种不同的涡旋，它们的区别在于它们的核中是否存在零能态。为了了解它们的起源，我们研究了塞曼耦合和超导配对的相互作用，在三维金属带反转。弱塞曼场被发现抑制轨道内自旋单态配对，已知本地化的表面上的涡旋的末端的状态。另一方面，一个轨道三重态配对被证明是稳定的塞曼相互作用，但导致离域的零能量马约拉纳模式延伸通过涡旋。与此相反，有限能量的涡旋模式保持本地化的涡旋两端，即使当配对是轨道三重态的形式。现象上，这表现为观察到的零偏置峰内的拓扑涡旋的核心时，所施加的磁场的增加消失。FeTe（1-x）Sex中磁性杂质的存在会被吸引到涡旋上，这会导致在一小部分涡旋中产生这种塞曼诱导的Majorana模的离域，这些涡旋捕获了足够多的磁性杂质。我们的研究结果提供了一个解释的二分法拓扑和非拓扑涡旋最近观察到的FeTe（1-x）性别。
In the superconducting regime of FeTe(1-x)Sex, there exist two types of vortices which are distinguished by the presence or absence of zero-energy states in their core. To understand their origin, we examine the interplay of Zeeman coupling and superconducting pairings in three-dimensional metals with band inversion. Weak Zeeman fields are found to suppress intraorbital spin-singlet pairing, known to localize the states at the ends of the vortices on the surface. On the other hand, an orbital-triplet pairing is shown to be stable against Zeeman interactions, but leads to delocalized zero-energy Majorana modes which extend through the vortex. In contrast, the finite-energy vortex modes remain localized at the vortex ends even when the pairing is of orbital-triplet form. Phenomenologically, this manifests as an observed disappearance of zero-bias peaks within the cores of topological vortices upon an increase of the applied magnetic field. The presence of magnetic impurities in FeTe(1-x)Sex, which are attracted to the vortices, would lead to such Zeeman-induced delocalization of Majorana modes in a fraction of vortices that capture a large enough number of magnetic impurities. Our results provide an explanation for the dichotomy between topological and nontopological vortices recently observed in FeTe(1-x)Sex.