School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA.
Department of Physics, Condensed Matter Theory Center and Joint Quantum Institute, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev Lett. 2019 Feb 1;122(4):047003. doi: 10.1103/PhysRevLett.122.047003.
We report anomalous enhancement of the critical current at low temperatures in gate-tunable Josephson junctions made from topological insulator BiSbTeSe_{2} nanoribbons with superconducting Nb electrodes. In contrast to conventional junctions, as a function of the decreasing temperature T, the increasing critical current I_{c} exhibits a sharp upturn at a temperature T_{} around 20% of the junction critical temperature for several different samples and various gate voltages. The I_{c} vs T demonstrates a short junction behavior for T>T_{}, but crosses over to a long junction behavior for T<T_{*} with an exponential T dependence I_{c}∝exp(-k_{B}T/δ), where k_{B} is the Boltzmann constant. The extracted characteristic energy scale δ is found to be an order of magnitude smaller than the induced superconducting gap of the junction. We attribute the long-junction behavior with such a small δ to low-energy Andreev bound states arising from winding of the electronic wave function around the circumference of the topological insulator nanoribbon.
我们报告了在具有超导 Nb 电极的拓扑绝缘体 BiSbTeSe2纳米带的栅极可调谐约瑟夫森结中低温下临界电流的异常增强。与传统结不同，作为温度 T 的函数，对于几个不同的样品和各种栅极电压，临界电流 Ic在温度 T处约为结临界温度的 20%时急剧上升。对于 T>T，Ic与 T 的关系表现为短结行为，但对于 T<T*，Ic与 T 呈指数关系，Ic∝exp(-kBT/δ)，其中 kB是玻尔兹曼常数。发现提取的特征能量标度 δ 比结的诱导超导能隙小一个数量级。我们将这种小 δ 的长结行为归因于源自拓扑绝缘体纳米带周长的电子波函数缠绕的低能安德烈夫束缚态。
