From Yu-Shiba-Rusinov states to Majorana zero modes

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From YSR states to Majorana zero mode
2022. 11. 11. 10:15
BME building F, seminar room of the Dept. of Theoretical Physics
Bendegúz Nyári (BME)
The Majorana fermion was originally proposed by Ettore Majorana in 1937 as an elementary particle which is its own antiparticle. Although this elementary particle has not yet been detected, its analogons, Majorana states (and Majorana Zero Modes, often called Majoranas) can appear as quasiparticle excitations in condensed matter physics. These latter have promising applications as building blocks of topological quantum bits, based on their non-Abelian anyonic exchange statistics. Thanks to the rapid development in scanning-tunneling microscopy techniques, today it is possible to build the systems used in model calculations that should host Majoranas, and measure their spectral properties. It remains challenging to prove the presence of Majoranas from the data, and ab initio calculations can help arrive at definite conclusions.
I will present an overview of our ab initio based results on the formation of Majorana zero modes. I will start from a single magnetic impurity on the surface of an s-wave superconductor,  introduce the Yu-Shiba-Rusinov states, and then move on to magnetic chains. For some spin-spiral configurations we found an induced minigap, which has zero energy states localized to the ends of the chain in a spin triplet (superconducting) state. By varying the spiraling angle we observed a phase transition to another gapped state without zero energy states, which we expect to be a topological phase transition.