Iron-based superconductors as a new Majorana playground

Majorana zero modes (MZMs) in solid materials and devises have attracted tremendous interest owing to their non-Abelian statistics and potential applications in topological quantum computation. Last ten years witness rapid progresses and serious setbacks in searching for MZMs. Recently iron-based superconductors emerged as a new and promising Majorana playground due to relatively high temperature and high purity. In this talk I will report a series of our discoveries which help to establish this iron-based Majorana platform. We have observed a superconducting topological surface state of Fe(Te, Se) with Tc ~ 15K by using ARPES [1], and a pristine MZM inside a vortex core of this material by using STM [2]. We have also observed a half-integer level shift of vortex bound states [3] and nearly quantized Majorana conductance [4] in this material, which are hallmarks of MZMs. We have also found that most of iron-based superconductors [5], including monolayer Fe(Te, Se)/STO [6], have similar topological electronic structures. One of them, CaKFe4As4, an Fe-As bilayer superconductor (Tc ~ 35K), is found to possess MZM and other bound states that can be well reproduced by a simple theoretical model [7]. In addition, we found that impurities and pressure can be used as tuning methods to control MZMs in iron-based superconductors [8,9]. The combination of intrinsic topological nature of vortex and large energy spacing among the discreet bound states inside these vortices proves the Majorana nature of vortex zero-modes discovered in the iron-based superconductors, thus creating an exciting playground for realizing and manipulating Majorana modes [10].
References
[1] Peng Zhang et al., Science 360, 182 (2018)
[2] Dongfei Wang et al., Science 362, 334 (2018)
[3] Lingyuan Kong et al., Nature Physics 15, 1181 (2019)
[4] Shiyu Zhu et al., Science 367, 189 (2020)
[5] Peng Zhang et al., Nature Physics 15, 41 (2019)
[6] Xun Shi et al., Science Bulletin 62, 503 (2017)
[7] Wenyao Liu et al., Nature Communications 11, 5688 (2020)
[8] Peng Fan et al., Nature Communications 12, 1348 (2021)
[9] Lingyuan Kong et al., Nature Communications 12, 4146 (2021)
[10] Lingyuan Kong and Hong Ding, Acta Physica Sinica 69, 110301 (2020)