About 80 years ago, physicist Ettore Majorana proposed the existence of fermions that are their own antiparticles. Now, these Majorana fermions are attracting a lot of attention for their potential use in certain quantum computing applications. While it is possible to create Majorana-fermion-like states in a topological superconductor, it is very difficult to do so cleanly because of large Fermi energies or the required impurities in the material. Here, we experimentally break through this difficulty.

Majorana fermions can be realized as a bound state at zero energy, known as a Majorana zero mode (MZM). Using scanning tunneling spectroscopy, we detect the unique signature of a MZM in defect-free regions of the topological superconductor (Li0.84Fe0.16)OHFeSe. The intrinsic nontrivial topology of this system enables the realization of a MZM without the need to introduce impurities in the FeSe layer, which was a requirement in previous work.

Our work presents an ideal and practical platform to further study the properties of MZMs, explore their manipulation, and construct MZM-based quantum bits, all of which opens a new, clear route to rapid progress in the fundamental understanding and potential applications of MZMs.
This work has been published in Phys. Rev. X 8, 041056, 2018.