Majorana zero modes (MZMs) are spatially-localized zero-energy fractional quasiparticles with non-Abelian braiding statistics. They are believed to hold great promise for topological quantum computing. By using low-temperature and strong-magnetic-field scanning tunneling microscopy/spectroscopy, a breakthrough of Majorana zero mode has been firstly achieved in a single material platform of high-Tc iron-based superconductor, FeTe0.55Se0.45. The mechanism of two distinct classes of vortices presented in this system was revealed, which directly tied with the presence or absence of zero-bias peak. We further found the Majorana conductance plateau in vortices. Both the extrinsic instrumental convoluted broadening and the intrinsic quasiparticle poisoning can reduce the conductance plateau value, and when extrinsic instrumental broadening is removed by deconvolution, the plateau nearly reaches a 2e2/h quantized value. Moreover, we confirmed the existence of MZMs in the vortex cores of CaKFe4As4 and LiFeAs. Based on these works mentioned above, most recently, we have successfully achieved the large-scale, highly-ordered and tunable MZM lattice in strained LiFeAs. Notably, more than 90% of the vortices are topological and possess the characteristics of isolated MZMs at the vortex center, forming ordered MZM lattice with the density and the geometry tunable by external magnetic field. With decreasing the spacing of neighboring vortices, the MZMs start to couple with each other. Our results show a great potential of MZMs in the application of topological quantum computations in the future.
We gratefully acknowledge helpful discussions with our collaborators. Genda Gu (BNL), Changqing Jin (IOP, CAS), and Haitao Yang (IOP, CAS) provided high-quality single-crystal samples. Hong Ding (SJTU) carried out the ARPES measurements. Geng Li, Hui Chen, Shiyu Zhu, and Li Huang performed the STM/STS measurements. Ziqiang Wang (BC) and Liang Fu (MIT) contributed valuable theoretical insights.
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