拓扑半金属-超导体异质结的约瑟夫森效应

Josephson effect in topological semimetal-superconductor heterojunctions

拓扑半金属是一类受对称性保护的无能隙量子材料.因其相对论性能带色散关系,拓扑半金属中涌现出丰富的量子态和量子效应,例如费米弧表面态和手征反常.近年来,因在拓扑量子计算的潜在应用,拓扑与超导的耦合体系受到广泛关注.本文从两方面回顾拓扑半金属-超导体异质结体系近年来的实验进展:1)超导电流对拓扑量子态的模式过滤;2)拓扑超导和Majorana零能模的探测与调控.对于前者,利用约瑟夫森电流对电磁场的响应,拓扑半金属中费米弧表面态的弹道输运被揭示,高阶拓扑半金属相被证实,有限动量配对及超导二极管效应被实现.对于后者,通过交流约瑟夫森效应,狄拉克半金属中4π周期的拓扑超导态被发现,纯电学栅压调控的拓扑相变被实现.本文最后展望了拓扑半金属-超导体异质结体系的发展前景和在Majorana零能模编织和拓扑量子计算上的潜在应用.

Topological semimetals are exotic phases of quantum matter with gapless electronic excitation protected by symmetry.Benefitting from its unique relativistic band dispersion,topological semimetals host abundant quantum states and quantum effects,such as Fermi-arc surface states and chiral anomaly.In recent years,due to the potential application in topological quantum computing,the hybrid system of topology and superconductivity has aroused wide interest in the community.Recent experimental progress of topological semimetal-superconductor heterojunctions is reviewed in two aspects:1)Josephson current as a mode filter of different topological quantum states;2)detection and manipulation of topological superconductivity and Majorana zero modes.For the former,utilizing Josephson interference,ballistic transport of Fermi-arc surface states is revealed,higher-order topological phases are discovered,and finite-momentum Cooper pairing and superconducting diode effect are realized.For the latter,by detecting a.c.Josephson effect in Dirac semimetals,the 4π-periodic supercurrent is discovered.By all-electric gate control,the topological transition of superconductivity is obtained.Outlooks of future research on topological semimetal-superconductor heterojunctions and their application in Majorana braiding and topological quantum computing are discussed.