Tuning interactions between spins in a superconductor
Tuning interactions between spins in a superconductor
复制标题
DOI：
10.1073/pnas.2024837118
复制
发表时间：
2021-04-06
影响因子：
11.1
通讯作者：
Yazdani, Ali
中科院分区：
文献类型：
--
作者：
Ding, Hao;Hu, Yuwen;Yazdani, Ali
新颖的多体和拓扑电子相可以在耦合到超导体的相互作用自旋的组件中创建，例如末端具有马约拉纳零模式（MZM）的一维拓扑超导体。理解和控制自旋与它们在超导体中引起的带隙内 Yu-Shiba-Rusinov (YSR) 态的新兴能带结构之间的相互作用是设计此类相的基础。在这里，通过使用扫描隧道显微镜 (STM) 精确定位磁性吸附原子，我们展示了自旋之间交换相互作用的可调性以及它们在铋 (Bi) 薄膜表面诱导的 YSR 态杂化的精确控制，该薄膜通过邻近效应实现超导。在这个平台中，根据自旋的分离，Ruderman-Kittel-Kasuya-Yosida (RKKY) 相互作用、自旋轨道耦合和表面磁各向异性之间的相互作用稳定了不同类型的自旋排列。我们使用毫开尔文温度下的高分辨率 STM 光谱，通过监测自旋诱导的 YSR 状态及其能量分裂来探测这些自旋排列。这些测量还揭示了超导体中一对自旋具有不同电子数奇偶性的基态之间的量子相变，这些自旋通过它们的分离来调节。对较大组件的实验表明，自旋-自旋相互作用可以在超导体中长距离介导。我们的结果表明，控制该平台中 YSR 态的杂化提供了设计此类态的能带结构以创建拓扑相的可能性。
Novel many-body and topological electronic phases can be created in assemblies of interacting spins coupled to a superconductor, such as one-dimensional topological superconductors with Majorana zero modes (MZMs) at their ends. Understanding and controlling interactions between spins and the emergent band structure of the in-gap Yu-Shiba-Rusinov (YSR) states they induce in a superconductor are fundamental for engineering such phases. Here, by precisely positioning magnetic adatoms with a scanning tunneling microscope (STM), we demonstrate both the tunability of exchange interaction between spins and precise control of the hybridization of YSR states they induce on the surface of a bismuth (Bi) thin film that is made superconducting with the proximity effect. In this platform, depending on the separation of spins, the interplay among Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, spin-orbit coupling, and surface magnetic anisotropy stabilizes different types of spin alignments. Using high-resolution STM spectroscopy at millikelvin temperatures, we probe these spin alignments through monitoring the spin-induced YSR states and their energy splitting. Such measurements also reveal a quantum phase transition between the ground states with different electron number parity for a pair of spins in a superconductor tuned by their separation. Experiments on larger assemblies show that spin-spin interactions can be mediated in a superconductor over long distances. Our results show that controlling hybridization of the YSR states in this platform provides the possibility of engineering the band structure of such states for creating topological phases.