Qin Wei, Zhang Zhenyu
International Center for Quantum Design of Functional Materials (ICQD), Hefei National Laboratory for Physical Sciences at the Microscale (HFNL), and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Phys Rev Lett. 2014 Dec 31;113(26):266806. doi: 10.1103/PhysRevLett.113.266806.
At the interface of an s-wave superconductor and a three-dimensional topological insulator, Majorana zero modes and Majorana helical states have been proposed to exist respectively around magnetic vortices and geometrical edges. Here we first show that randomly distributed magnetic impurities at such an interface will induce bound states that broaden into impurity bands inside (but near the edges of) the superconducting gap, which remains open unless the impurity concentration is too high. Next we find that an increase in the superconducting gap suppresses both the oscillation magnitude and the period of the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities. Within a mean-field approximation, the ferromagnetic Curie temperature is found to be essentially independent of the superconducting gap, an intriguing phenomenon due to a compensation effect between the short-range ferromagnetic and long-range antiferromagnetic interactions. The existence of robust superconductivity and persistent ferromagnetism at the interface allows realization of a novel topological phase transition from a nonchiral to a chiral superconducting state at sufficiently low temperatures, providing a new platform for topological quantum computation.
在s波超导体与三维拓扑绝缘体的界面处，人们提出马约拉纳零模和马约拉纳螺旋态分别存在于磁涡旋和几何边缘附近。在这里，我们首先表明，在这样的界面处随机分布的磁性杂质会诱导出束缚态，这些束缚态会展宽成超导能隙内部（但靠近边缘）的杂质带，除非杂质浓度过高，超导能隙仍会保持开放。接下来我们发现，超导能隙的增加会抑制两个磁性杂质之间的鲁德曼-基特尔-卡苏亚-约西达相互作用的振荡幅度和周期。在平均场近似下，发现铁磁居里温度基本上与超导能隙无关，这是一个由于短程铁磁和长程反铁磁相互作用之间的补偿效应而产生的有趣现象。界面处稳健的超导性和持久的铁磁性的存在使得在足够低的温度下能够实现从非手性超导态到手性超导态的新型拓扑相变，为拓扑量子计算提供了一个新平台。
