Scanning tunneling spectroscopy of vortex core states in Fe(Se,Te) using superconducting STM tip*

In iron-based superconductors with topological surface states, the proximity effect of the bulk superconductivity to the surface states induces topological superconductivity at the surface, giving rise to the emergence of the Majorana quasiparticle at a vortex core. Although the recent scanning tunneling microscopy (STM) experiments have revealed the zero-energy vortex bound states (ZVBS) suggestive of the Majorana zero mode (MZM) at the vortex cores of various iron-based superconductors [1,2], it has been still elusive whether the observed ZVBSs are the MZM or not. In this study, we focus on the predicted spin polarization of the MZM, which is a peculiar nature of MZM and have conducted the spin-polarized spectroscopy around vortex cores of FeSe_0.4Te_0.6 at a magnetic field of 1.5 T, using superconducting Nb STM tip with Zeeman-split coherence peaks. The spectra along a path through a vortex core indicate spatially non-dispersive two pairs of peaks at the energies of Zeeman-split coherence peaks of the STM tip, assuring that these spectra capture the ZVBS. We will discuss the spin-polarization of the observed ZVBS in the presentation. 

References

[1] D. Wang et al., Science 362, 333 (2018).

[2] T. Machida et al., Nat. Mater. 18, 811 (2019).