单个磁性杂质与超导体耦合的调谐：量子相变和输运
Tuning the coupling of an individual magnetic impurity to a superconductor: quantum phase transition and transport
摘要：
超导体上磁性吸附物的交换散射产生Yu-Shiba-Rusinov（YSR）束缚态。根据交换耦合的强度，磁矩对库珀对凝聚体的扰动很弱，导致自由自旋基态，或者在其附近结合准粒子，导致（部分）屏蔽自旋态。在这里，我们利用吸附在Pb（111）表面上的Fe-卟啉分子的灵活性，可逆地和连续地在这些不同的基态之间进行调谐。我们发现，FeP时刻屏蔽在原始吸附状态。接近扫描隧道显微镜的尖端，我们施加足够强的吸引力来调节分子通过量子相变进入自由自旋状态。我们确定和表征的过渡，通过调查的传输过程作为功能的尖端分子距离，激发单电子隧穿以及（多）Andreev反射的YSR状态。
英文摘要：
The exchange scattering at magnetic adsorbates on superconductors gives rise to Yu-Shiba-Rusinov (YSR) bound states. Depending on the strength of the exchange coupling, the magnetic moment perturbs the Cooper pair condensate only weakly, resulting in a free-spin ground state, or binds a quasiparticle in its vicinity, leading to a (partially) screened spin state. Here, we use the flexibility of Fe-porphin molecules adsorbed on a Pb(111) surface to reversibly and continuously tune between these distinct ground states. We find that the FeP moment is screened in the pristine adsorption state. Approaching the tip of a scanning tunneling microscope, we exert a sufficiently strong attractive force to tune the molecule through the quantum phase transition into the free-spin state. We ascertain and characterize the transition by investigating the transport processes as function of tip-molecule distance, exciting the YSR states by single-electron tunneling as well as (multiple) Andreev reflections.
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