Liebhaber Eva, Rütten Lisa M, Reecht Gaël, Steiner Jacob F, Rohlf Sebastian, Rossnagel Kai, von Oppen Felix, Franke Katharina J
Fachbereich Physik, Freie Universität Berlin, 14195, Berlin, Germany.
Dahlem Center for Complex Quantum Systems and Fachbereich Physik, Freie Universität Berlin, 14195, Berlin, Germany.
Nat Commun. 2022 Apr 20;13(1):2160. doi: 10.1038/s41467-022-29879-0.
Magnetic adatom chains on surfaces constitute fascinating quantum spin systems. Superconducting substrates suppress interactions with bulk electronic excitations but couple the adatom spins to a chain of subgap Yu-Shiba-Rusinov (YSR) quasiparticles. Using a scanning tunneling microscope, we investigate such correlated spin-fermion systems by constructing Fe chains adatom by adatom on superconducting NbSe. The adatoms couple entirely via the substrate, retaining their quantum spin nature. In dimers, we observe that the deepest YSR state undergoes a quantum phase transition due to Ruderman-Kittel-Kasuya-Yosida interactions, a distinct signature of quantum spins. Chains exhibit coherent hybridization and band formation of the YSR excitations, indicating ferromagnetic coupling. Longer chains develop separate domains due to coexisting charge-density-wave order of NbSe. Despite the spin-orbit-coupled substrate, we find no signatures of Majoranas, possibly because quantum spins reduce the parameter range for topological superconductivity. We suggest that adatom chains are versatile systems for investigating correlated-electron physics and its interplay with topological superconductivity.
表面上的磁性吸附原子链构成了迷人的量子自旋系统。超导衬底抑制了与体电子激发的相互作用，但将吸附原子的自旋与亚能隙的汤川-志田-鲁西诺夫（YSR）准粒子链耦合起来。我们使用扫描隧道显微镜，通过在超导NbSe₂上逐个吸附原子构建铁链，来研究这种相关的自旋-费米子系统。吸附原子完全通过衬底相互耦合，保持其量子自旋性质。在二聚体中，我们观察到最深的YSR态由于Ruderman-Kittel-Kasuya-Yosida相互作用而经历量子相变，这是量子自旋的一个独特特征。链表现出YSR激发的相干杂化和能带形成，表明存在铁磁耦合。由于NbSe₂中共存的电荷密度波序，较长的链会形成单独的畴。尽管衬底存在自旋-轨道耦合，但我们没有发现马约拉纳费米子的迹象，这可能是因为量子自旋缩小了拓扑超导的参数范围。我们认为吸附原子链是研究关联电子物理学及其与拓扑超导相互作用的通用系统。
