Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe<sub>0.55</sub>Se<sub>0.45</sub>

By using scanning tunneling microscopy (STM) we find and characterize dispersive, energy symmetric in-gap states in the iron-based superconductor FeTe_0.55Se_0.45, a material that exhibits signatures of topological superconductivity, and Majorana bound states at vortex cores or at impurity locations. We use a superconducting STM tip for enhanced energy resolution, which enables us to show that impurity states can be tuned through the Fermi level with varying tip-sample distance. We find that the impurity state is of the Yu-Shiba-Rusinov (YSR) type, and argue that the energy shift is caused by the low superfluid density in FeTe_0.55Se_0.45, which allows the electric field of the tip to slightly penetrate the sample. We model the newly introduced tip-gating scenario within the single-impurity Anderson model and find good agreement to the experimental data.

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Bulletin of the American Physical Society

APS March Meeting 2021

Volume 66, Number 1

Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA

Session P54: Fe-Based Superconductors: Quantum Criticality and Topology

Abstract: P54.00007 : Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe0.55Se0.45

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Abstract: P54.00007 : Spatially dispersing Yu-Shiba-Rusinov states in the unconventional superconductor FeTe_0.55Se_0.45