Department of Physics, Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
Nat Commun. 2013;4:1689. doi: 10.1038/ncomms2701.
Coupling the surface state of a topological insulator to an s-wave superconductor is predicted to produce the long-sought Majorana quasiparticle excitations. However, superconductivity has not been measured in surface states when the bulk charge carriers are fully depleted, that is, in the true topological regime relevant for investigating Majorana modes. Here we report measurements of d.c. Josephson effects in topological insulator-superconductor junctions as the chemical potential is moved through the true topological regime characterized by the presence of only surface currents. We compare our results with three-dimensional quantum transport simulations, and determine the effects of bulk/surface mixing, disorder and magnetic field; in particular, we show that the supercurrent is largely carried by surface states, due to the inherent topology of the bands, and that it is robust against disorder. Our results thus clarify key open issues regarding the nature of supercurrents in topological insulators.
将拓扑绝缘体的表面态与 s 波超导体耦合，预计会产生长期寻求的马约拉纳准粒子激发。然而，当体电荷载流子完全耗尽时，即在真正与研究马约拉纳模式相关的拓扑区域，尚未在表面态中测量到超导性。在这里，我们报告了在通过仅存在表面电流的真正拓扑区域移动化学势时，拓扑绝缘体-超导体结的直流约瑟夫森效应的测量结果。我们将我们的结果与三维量子输运模拟进行了比较，并确定了体/表面混合、无序和磁场的影响；特别是，我们表明由于能带的固有拓扑，超导电流主要由表面态承载，并且对无序具有鲁棒性。因此，我们的结果阐明了有关拓扑绝缘体中超导电流本质的关键未决问题。
