Dartiailh Matthieu C, Cuozzo Joseph J, Elfeky Bassel H, Mayer William, Yuan Joseph, Wickramasinghe Kaushini S, Rossi Enrico, Shabani Javad
Department of Physics, Center for Quantum Phenomena, New York University, New York, NY, 10003, USA.
Department of Physics, William & Mary, Williamsburg, VA, 23187, USA.
Nat Commun. 2021 Jan 4;12(1):78. doi: 10.1038/s41467-020-20382-y.
Josephson junctions hosting Majorana fermions have been predicted to exhibit a 4π periodic current phase relation. One experimental consequence of this periodicity is the disappearance of odd steps in Shapiro steps experiments. Experimentally, missing odd Shapiro steps have been observed in a number of materials systems with strong spin-orbit coupling and have been interpreted in the context of topological superconductivity. Here we report on missing odd steps in topologically trivial Josephson junctions fabricated on InAs quantum wells. We ascribe our observations to the high transparency of our junctions allowing Landau-Zener transitions. The probability of these processes is shown to be independent of the drive frequency. We analyze our results using a bi-modal transparency distribution which demonstrates that only few modes carrying 4π periodic current are sufficient to describe the disappearance of odd steps. Our findings highlight the elaborate circumstances that have to be considered in the investigation of the 4π Josephson junctions in relationship to topological superconductivity.
理论预测，承载马约拉纳费米子的约瑟夫森结会呈现出4π周期的电流相位关系。这种周期性的一个实验结果是，在夏皮罗台阶实验中奇数台阶消失。在实验中，人们在许多具有强自旋轨道耦合的材料系统中观察到了缺失的奇数夏皮罗台阶，并在拓扑超导的背景下对其进行了解释。在此，我们报告在砷化铟量子阱上制备的拓扑平凡约瑟夫森结中出现的缺失奇数台阶。我们将观察结果归因于结的高透明度，这使得朗道-齐纳跃迁得以发生。这些过程的概率被证明与驱动频率无关。我们使用双峰透明度分布来分析结果，这表明只有少数携带4π周期电流的模式就足以描述奇数台阶的消失。我们的研究结果突出了在研究与拓扑超导相关的4π约瑟夫森结时必须考虑的复杂情况。
