Uldemolins M, Mesaros A, Gu G D, Palacio-Morales A, Aprili M, Simon P, Massee F
Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, Orsay, France.
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA.
Nat Commun. 2024 Oct 2;15(1):8526. doi: 10.1038/s41467-024-52847-9.
Understanding the interplay between individual magnetic impurities and superconductivity is crucial for bottom-up construction of novel phases of matter. Sub-gap bound states that are used in this endeavor are typically considered as independent entities that each result from the exchange scattering between the respective impurity orbitals and electrons of the superconducting condensate. Here we present experimental evidence of individual multi-spin impurities where the sub-gap states are not independent. Specifically, we find that by tuning the energy of the state closest to zero through zero, all other sub-gap states change particle-hole asymmetry as well. We show that this can be understood by including Hund's coupling, which favors high-spin configurations, into a multi-orbital Anderson model. Unlike for the case of independent spins, the transition we observe signals the simultaneous departure of more than one quasiparticle from the impurity, while the parity of the ground state may remain unchanged. Our results show that Hund's coupling is not only crucial in generating high-spin impurities, but also to understand the transition between two distinct ground states, and should therefore be taken into account for e.g. impurity-based band-structure engineering.
理解单个磁性杂质与超导性之间的相互作用对于自下而上构建新型物质相至关重要。在此过程中使用的亚能隙束缚态通常被视为独立实体，每个态都源于各自杂质轨道与超导凝聚态电子之间的交换散射。本文我们给出了亚能隙态并非独立的单个多自旋杂质的实验证据。具体而言，我们发现通过将最接近零的态的能量调至零，所有其他亚能隙态的粒子 - 空穴不对称性也会改变。我们表明，通过将有利于高自旋构型的洪德耦合纳入多轨道安德森模型，可以理解这一现象。与独立自旋的情况不同，我们观察到的转变表明不止一个准粒子同时从杂质处离开，而基态的宇称可能保持不变。我们的结果表明，洪德耦合不仅在产生高自旋杂质方面至关重要，而且对于理解两个不同基态之间的转变也很关键，因此例如在基于杂质的能带结构工程中应予以考虑。
