Majorana spin in magnetic atomic chain systems

Abstract

Magnetic atomic chains grown on top of conventional superconductors may form an interesting and promising platform for the study of Majorana zero modes. Despite the strong evidence already provided with a state-of-art scanning tunneling microscope (STM) technique, clear features beyond the energetic and spatial ones are required to exclude the only remaining alternative interpretation of the zero modes as trivial Shiba states accidentally occurring at zero energy. The authors here propose a robust spin signature for this purpose. This signature is rooted in two sum rules that dictate the distribution of spin densities in a superconducting state with respect to a normal state, and has been recently detected with spin-polarized STM technique that implicitly takes advantage of the sum rules.