Press release

Tailored chains for Majorana bound states

Our research group revealed signatures of Majorana bound states in atom-by-atom constructed chains of cobalt and iron atoms. The results help to distinguish the interesting Majorana bound states from trivial states in the gap of the superconductor. The study appeared in Nature Communications.

Majorana particles are exotic elementary particles which are identical to their antiparticles. They have been predicted more than 80 years ago by the Italian theoretician Ettore Majorana, but could not be experimentally verified by particle physicists up to now. In recent years, several research groups either theoretically predicted or found experimental signatures of the analogues of Majorana elementary particles in solid state systems, the so-called Majorana bound states.

In collaboration with a theory group of the Forschungszentrum Jülich, we were now able to reveal signatures of Majorana bound states right at the transition between a chain of iron atoms and a chain of cobalt atoms which were built using the tip of a scanning tunneling microscope on the clean surface of a superconducting rhenium crystal. Chains as long as 100 atoms have been realized merely limited by surface defects and the number of available atoms that can be found in the environment.

By terminating the magnetic iron chains with the nonmagnetic cobalt chains we attenuated parasitic trivial electronic states, the so-called Yu-Shiba-Rusinov states, which hamper the identification of Majorana bound states. Combining the two materials, a sharp transition between a spiral magnetic phase in the iron chain and a nonmagnetic superconducting phase in the cobalt chain was realized, which leads to a more pronounced signature of a Majorana bound state at both ends of the iron chain.

Figure: Three-dimensional rendered view of a scanning tunneling microscope image showing a chain of 20 iron atoms (Fe) and five cobalt atoms (Co) on both ends, which have been assembled on the surface of a superconducting rhenium (Re) single crystal. The bright halos represent an artistic view of the signal measured at the Fermi energy.

Original publication:

Lucas Schneider, Sascha Brinker, Manuel Steinbrecher, Jan Hermenau, Thore Posske, Manuel dos Santos Dias, Samir Lounis, Roland Wiesendanger, and Jens Wiebe,
Controlling in-gap end states by linking nonmagnetic atoms and artificially-constructed spin chains on superconductors,
Nature Communications 11, 4707 (2020).
DOI: https://doi.org/10.1038/s41467-020-18540-3

Further Information:

Prof. Dr. Prof. h.c. Dr. h.c. Roland Wiesendanger 
Department of Physics
University of Hamburg
Phone: 040 / 42838-5244
E-Mail: wiesendanger@physnet.uni-hamburg.de