Thupakula U, Perrin V, Palacio-Morales A, Cario L, Aprili M, Simon P, Massee F
Laboratoire de Physique des Solides (CNRS UMR 8502), Bâtiment 510, Université Paris-Sud/Université Paris-Saclay, 91405 Orsay, France.
Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, F-44000 Nantes, France.
Phys Rev Lett. 2022 Jun 17;128(24):247001. doi: 10.1103/PhysRevLett.128.247001.
The pair breaking potential of individual magnetic impurities in s-wave superconductors generates localized states inside the superconducting gap commonly referred to as Yu-Shiba-Rusinov (YSR) states whose isolated nature makes them promising building blocks for artificial structures that may host Majorana fermions. One of the challenges in this endeavor is to understand their intrinsic lifetime, ℏ/Λ, which is expected to be limited by the inelastic coupling with the continuum thus leading to decoherence. Here we use shot-noise scanning tunneling microscopy to reveal that electron tunneling into superconducting 2H-NbSe_{2} mediated by YSR states is not Poissonian, but ordered as a function of time, as evidenced by a reduction of the noise. Moreover, our data show the concomitant transfer of charges e and 2e, indicating that incoherent single particle and coherent Andreev processes operate simultaneously. From the quantitative agreement between experiment and theory we obtain Λ=1 μeV≪k_{B}T demonstrating that shot noise can probe energy scales and timescales inaccessible by conventional spectroscopy whose resolution is thermally limited.
s波超导体中单个磁性杂质的配对破坏势在超导能隙内产生局域态，通常称为汤浅-芝-鲁西诺夫（YSR）态，其孤立特性使其成为可能容纳马约拉纳费米子的人工结构的理想构建块。这项工作面临的挑战之一是理解它们的固有寿命ℏ/Λ，预计其会受到与连续体的非弹性耦合的限制，从而导致退相干。在这里，我们使用散粒噪声扫描隧道显微镜来揭示，由YSR态介导的电子隧穿进入超导2H-NbSe₂并非泊松过程，而是随时间有序变化，这由噪声的降低所证明。此外，我们的数据显示伴随着电荷e和2e的转移，表明非相干单粒子和相干安德列夫过程同时发生。从实验与理论之间的定量一致性，我们得到Λ = 1 μeV≪kBT，这表明散粒噪声可以探测到传统光谱无法达到的能量尺度和时间尺度，传统光谱的分辨率受温度限制。
