Bi/Ni界面超导机制的研究

Since the discovery of interfacial superconductivity of Bi/Ni heterostructure, it has been receiving significant attentions from the condensed matter community. One of the reason is that Bi/Ni heterostructure is a unique typical system with coexistence of magnetism and superconductivity; the other is that the interfacial superconductivity of Bi/Ni heterostructure is highly possible to be unconventional with non-zero orbital angular momentum. It gives Bi/Ni substantial potential for applications in topological quantum computations. With respect to artificial hybrid structures, intrinsic unconventional superconductors, such as Bi/Ni heterostructure, have many advantages including flexibility in device design, convenience in device fabrications, etc.. It makes themselves more suitable for constructing topological quantum computers. However, up till now, the mechanism of superconductivity for Bi/Ni interfaces is still under debate, being either p-wave or d-wave pairings. In this proposal, the applicant plans to construct mesoscopic devices making use of nanofabrication techniques and conduct a series of quantum transport experiments, including detecting density of edge states by tunneling measurements, detecting edge current by fabricating local superconducting quantum interference device (SQUID), exploring anisotropy of superconducting order parameters by phase-sensitive SQUID experiments. The mechanism of superconductivity for Bi/Ni interface will be determined by these experiments, and we will further search for routes to realize topological quantum computation based on the superconducting interface of Bi/Ni heterostructures.

Bi/Ni界面超导自发现以来，逐步受到凝聚态物理领域的重点关注。原因之一是Bi/Ni异质结是一个磁性与超导共存的典型体系，原因之二是Bi/Ni界面超导很有可能是具有非零轨道角动量的非常规超导 - 这使得它在拓扑量子计算方面有可观的潜在应用价值。相对于人工复合结构来说，Bi/Ni界面这种本征超导体具有器件设计灵活、制备难度低等优点，更利于构造拓扑量子计算机。然而到目前为止，它的超导配对机制还没有被完全确定，有可能是p波或者d波超导。在本研究计划中，申请人拟利用微纳加工技术构建介观器件，开展一系列量子输运实验，包括利用隧穿电输运实验测量边界态密度、利用局域SQUID探测边界电流、利用相敏超导量子干涉实验确定超导序参量的各向异性。申请人计划通过这些实验确定Bi/Ni超导配对机制，并且寻求利用界面超导这种本征非常规超导体构造拓扑量子计算器件的途径。

在本项目的支持下，项目负责人开展了极低温条件下低维电子系统超导及相关量子效应研究，针对薄膜超导的机理及调控手段、氧化物界面低维电子系统拓扑能带结构调控等研究方向从电输运角度开展了系统性研究。研究发现了TiO在0.5K以下存在超导电性，并结合理论说明了其超导的形成机制；深入研究了VN薄膜的巡游电子来源及超导特性，并演示了应力对于超导转变温度的调控作用；研究了EuTiO3/KTaO3氧化物异质结界面处低维电子系统的输运性质，发现EuTiO3的反铁磁序及拓扑能带结构对于处于KTaO3内部但接近界面处的二维电子系统的输运性质具有显著的调制作用。本项目所支持的研究对于低维电子系统的超导以及与非常规性质之间的关联做了详细深入的研究，并发展了相应的超导调控手段，从基础研究和应用研究两方面都具有重要意义。