Queiroz Raquel, Stern Ady
Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 7610001, Israel.
Phys Rev Lett. 2019 Jul 19;123(3):036802. doi: 10.1103/PhysRevLett.123.036802.
The surface of a higher order topological insulator comprises a two-dimensional topological insulator (TI) with broken inversion symmetry, whose mass is determined by the microscopic details of the surface such as surface potentials and termination. It hosts a helical mode pinned to selected hinges where the surface gap changes its sign. We study the effect of perturbations that break time reversal and particle conservation on this helical mode, such as a Zeeman field and a proximate superconductor. We find that in contrast to the helical modes of inversion symmetric TIs, which are gapped by these couplings, the helical modes at the hinges can remain gapless and spatially split. When this happens, the Zeeman field splits the helical mode into a chiral mode surrounding the magnetized region, and a superconductor results in a helical Majorana mode surrounding the superconducting region. The combination of the two might lead to the gapping of one of the chiral Majorana modes, and leave a single one-dimensional chiral Majorana mode around the superconducting island. We propose that the different topological states can be measured in electrical transport.
高阶拓扑绝缘体的表面包含一个具有破缺反演对称性的二维拓扑绝缘体（TI），其质量由表面的微观细节（如表面势和终止情况）决定。它拥有一个螺旋模式，该模式固定在选定的棱边上，在这些棱边上表面能隙会改变符号。我们研究了破坏时间反演和粒子守恒的微扰对这种螺旋模式的影响，例如塞曼场和邻近的超导体。我们发现，与反演对称TI的螺旋模式不同，反演对称TI的螺旋模式会因这些耦合而产生能隙，而棱边上的螺旋模式可以保持无隙且在空间上分裂。当这种情况发生时，塞曼场将螺旋模式分裂为围绕磁化区域的手征模式，而超导体则会在超导区域周围产生螺旋马约拉纳模式。两者的结合可能会导致其中一个手征马约拉纳模式产生能隙，并在超导岛周围留下单个一维手征马约拉纳模式。我们提出，可以在电输运中测量不同的拓扑态。
