Majorana zero modes in vortices of FeTeₓSe₁₋ₓ and LiFeAs, and Majorana Kramers pairs in 2D Weyl–superconductor heterostructures

Majorana zero modes (MZMs) are predicted to appear in the vortex cores of an s-wave superconductor hosting a topological surface Dirac cone. Iron-based superconductors such as FeTeₓSe₁₋ₓ and LiFeAs have therefore emerged as leading candidate platforms, where scanning tunneling spectroscopy has revealed robust zero-bias peaks (ZBPs) in a subset of vortex cores. In the first part of the talk, I will address two contrasting experimental observations: in FeTeₓSe₁₋ₓ, the fraction of vortices exhibiting ZBPs decreases with increasing magnetic field, whereas in naturally strained LiFeAs, vortices pinned to biaxial charge-density-wave stripes form an ordered lattice in which over 90% of the vortices host isolated ZBPs.

Building on a three-dimensional tight-binding model for FeTeₓSe₁₋ₓ and LiFeAs, I will show how vortex-core Majorana physics resolves these two puzzles in the ZBP statistics: the field-dependent ZBP yield in FeTeₓSe₁₋ₓ and the anomalously high ZBP rate in LiFeAs.

Beyond these class-D vortex MZMs, Majorana Kramers pairs with zero energy are a distinct species of Majoranas—unlike nanowire or vortex-core Majoranas—because they are protected by time-reversal symmetry (class DIII). Motivated by the recent experimental discovery of special Weyl semimetals, we propose a 2D Weyl-d-wave-superconductor heterostructure, in which the intrinsic edge-state asymmetry enables gate-controlled relocation of Majorana corner modes. By tuning the chemical potential across coupled blocks, we propose an adiabatic process for the movement and exchange of symmetry-protected zero modes without the need for magnetic fields.