Sun Zhixiang, Enayat Mostafa, Maldonado Ana, Lithgow Calum, Yelland Ed, Peets Darren C, Yaresko Alexander, Schnyder Andreas P, Wahl Peter
Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
1] Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany [2] School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK.
Nat Commun. 2015 Mar 30;6:6633. doi: 10.1038/ncomms7633.
In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin-orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine the possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low-temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization.
在非磁性块状材料中，反演对称性保护着自旋简并性。然而，如果块状晶体结构缺乏反演中心，自旋 - 轨道相互作用会消除自旋简并性，从而产生一种Rashba金属，其费米面呈现出复杂的自旋纹理。在超导Rashba金属中，由这些复杂自旋结构构建的配对波函数通常会同时包含单重态和三重态特征。在此，我们研究了非中心对称BiPd中序参量可能的三重态分量，首次在一种非中心对称超导体中结合了宏观表征、原子尺度的超低温扫描隧道谱以及相对论第一性原理计算。虽然BiPd的超导态在拓扑上看似平凡，与由单一各向同性s波能隙控制序参量的巴丁 - 库珀 - 施里弗理论一致，但我们表明该材料呈现出具有螺旋自旋极化的狄拉克锥表面态。
