Interplay between Superconductivity and Ferromagnetism on a Topological Insulator
Interplay between Superconductivity and Ferromagnetism on a Topological Insulator
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DOI：
10.1103/physrevb.81.184525
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发表时间：
2010-03
影响因子：
3.7
通讯作者：
J. Linder;Yukio Tanaka;T. Yokoyama;A. Sudbø;N. Nagaosa
中科院分区：
文献类型：
--
作者：
J. Linder;Yukio Tanaka;T. Yokoyama;A. Sudbø;N. Nagaosa
我们从理论上研究了拓扑绝缘体表面的邻近感应超导性和铁磁性。特别是，我们研究了这些现象之间的相互作用如何影响安德烈夫束缚态，同时也考虑到非常规配对的可能性。当比较自旋单重态和自旋三重态配对时，我们发现激发光谱存在质的差异，导致后一种情况下产生无间隙激发。研究了表面态的形成及其对磁化方向的依赖性，发现这些态是 ${d}_{xy}$ 波情况下的马约拉纳费米子，与拓扑平凡的高 ${T}_{c}$ 铜酸盐形成鲜明对比。我们研究了电导谱中此类状态的特征，并且还计算了当约瑟夫森结沉积在拓扑绝缘体顶部时在拓扑绝缘体表面流动的超电流。研究发现，当分隔超导组的区域是铁磁体时，电流表现出反常的电流相位关系，并且我们还表明，与金属情况相比，这种情况下的交换场不会在临界电流中引起 $0\text{\ensuremath{-}}\ensuremath{\pi}$ 振荡。与高${T}_{c}$铜酸盐类似，拓扑表面上零能表面态的存在导致临界电流的强烈低温增强。
We study theoretically proximity-induced superconductivity and ferromagnetism on the surface of a topological insulator. In particular, we investigate how the Andreev-bound states are influenced by the interplay between these phenomena, taking also into account the possibility of unconventional pairing. We find a qualitative difference in the excitation spectrum when comparing spin-singlet and spin-triplet pairing, leading to nongapped excitations in the latter case. The formation of surface states and their dependence on the magnetization orientation is investigated, and it is found that these states are Majorana fermions in the ${d}_{xy}$-wave case in stark contrast to the topologically trivial high-${T}_{c}$ cuprates. The signature of such states in the conductance spectra is studied, and we also compute the supercurrent which flows on the surface of the topological insulator when a Josephson junction is deposited on top of it. It is found that the current exhibits an anomalous current-phase relation when the region separating the superconducting banks is ferromagnetic, and we also show that in contrast to the metallic case the exchange field in such a scenario does not induce $0\text{\ensuremath{-}}\ensuremath{\pi}$ oscillations in the critical current. Similarly to the high-${T}_{c}$ cuprates, the presence of zero-energy surface states on the topological surface leads to a strong low-temperature enhancement of the critical current.