Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay Cedex, France.
Quantronics Group, Service de Physique de l'État Condensé (CNRS UMR 3680), IRAMIS, CEA-Saclay, 91191 Gif-sur-Yvette, France.
Phys Rev Lett. 2019 Feb 22;122(7):076802. doi: 10.1103/PhysRevLett.122.076802.
Demonstrating the topological protection of Andreev states in Josephson junctions is an experimental challenge. In particular the telltale 4π periodicity expected for the current phase relation has remained elusive, because of fast parity breaking processes. It was predicted that low temperature ac susceptibility measurements could reveal the topological protection of quantum spin Hall edge states by probing their low energy Andreev spectrum at finite frequency. We have performed such a microwave probing of a phase-biased Josephson junction built around a bismuth nanowire, a predicted second order topological insulator, and which was previously shown to host one-dimensional ballistic edge states. We find absorption peaks at the Andreev level crossings, whose temperature and frequency dependencies point to protected topological crossings with an accuracy limited by the electronic temperature of our experiment.
证明约瑟夫森结中安德烈夫态的拓扑保护是一个实验挑战。特别是由于快速的奇偶破坏过程，预期的电流相位关系的明显的 4π 周期性仍然难以捉摸。有人预测，低温交流磁化率测量可以通过在有限频率下探测其低能安德烈夫谱来揭示量子自旋霍尔边缘态的拓扑保护。我们对围绕铋纳米线（预测的二阶拓扑绝缘体）构建的相位偏置约瑟夫森结进行了这种微波探测，该结以前被证明存在一维弹道边缘态。我们在安德烈夫能级交叉处发现了吸收峰，其温度和频率依赖性表明存在受保护的拓扑交叉，其精度受到实验电子温度的限制。
