van Mullekom Niels P E, Verlhac Benjamin, van Weerdenburg Werner M J, Osterhage Hermann, Steinbrecher Manuel, Franke Katharina J, Khajetoorians Alexander A
Institute for Molecules and Materials, Radboud University, Nijmegen, Netherlands.
Fachbereich Physik, Freie Universität Berlin, Berlin, Germany.
Sci Adv. 2024 Oct 18;10(42):eadq0965. doi: 10.1126/sciadv.adq0965.
Excitations of individual and coupled spins on superconductors provide a platform to study quantum spin impurity models as well as a pathway toward realizing topological quantum computing. Here, we characterize, using ultralow temperature scanning tunneling microscopy/spectroscopy, the Yu-Shiba-Rusinov (YSR) states of individual manganese phthalocyanine molecules with high spin on an ultrathin lead film in variable transverse magnetic field. We observe two types of YSR excitations, depending on the adsorption geometry. Using a zero-bandwidth model, we detail the role of the magnetic anisotropy, spin-spin exchange, and Kondo exchange. We illustrate that one molecular type can be treated as an individual spin, whereas the other type is best described by a coupled spin system. Using the field dependence of the YSR excitations combined with modeling, we describe the quantum phase of each excitation type. These results provide an insight into the quantum nature of YSR excitations in magnetic field and a platform to study spin impurity models on superconductors in magnetic field.
超导体上单个和耦合自旋的激发为研究量子自旋杂质模型提供了一个平台，同时也是实现拓扑量子计算的一条途径。在这里，我们利用超低温扫描隧道显微镜/光谱技术，对可变横向磁场中超薄铅膜上具有高自旋的单个锰酞菁分子的宇-芝-鲁西诺夫（YSR）态进行了表征。根据吸附几何结构，我们观察到了两种类型的YSR激发。使用零带宽模型，我们详细阐述了磁各向异性、自旋-自旋交换和近藤交换的作用。我们表明，一种分子类型可视为单个自旋，而另一种类型最好用耦合自旋系统来描述。利用YSR激发的磁场依赖性并结合建模，我们描述了每种激发类型的量子相。这些结果为深入了解磁场中YSR激发的量子本质提供了思路，并为研究磁场中超导体上的自旋杂质模型提供了一个平台。
