The Zero-Energy Trap express
You're looking for a quiet room for an important conversation. You step into a space, and hear silence. But upon closer inspection, you find that in one corner the ventilation is simply broken, and in another there's a hole in the floor that absorbs sound. In much the same way, physicists hunt for Majorana zero modes — special excitations in superconductors that could become ideal building blocks for quantum computing. They are impervious to interference, like a conversation in a perfectly isolated room.
In the new study, researchers examined the surface of an iron-based superconductor, Fe(Te,Se). Using a scanning tunneling microscope sensitive to electron spin, they found near-zero-energy states at step edges and line defects. These states looked exactly like Majorana zero modes. But they turned out to be "silence from a malfunction"—topologically trivial Yu-Shiba-Rusinov states that arise from impurities.
Even in regions without visible defects, bound states with zero energy were found. Combined analysis, spatially and under magnetic field, showed that these, too, have nothing to do with Majorana fermions. It's like finding a perfectly quiet room but realizing the silence comes from a vacuum around it, not from good soundproofing. This work reminds us: without spin measurements, the race for a quantum computer risks running into a mirage.
Original abstract
as written by the authors arXiv:2606.17499
Majorana zero modes, which obey non-Abelian exchange statistics, are promising candidates for topological quantum computation due to their robustness against environmental perturbations. The iron-based superconductor Fe(Te,Se) has been identified as an intrinsic topological superconductor, possibly hosting Majorana zero modes. In this paper, we report the observation of near-zero-energy localized states at multiple structural defects on the Fe(Te,Se) surface, which could be misidentified as Majorana zero modes without additional verification. By using spin-polarized scanning tunneling spectroscopy, we demonstrate that the near-zero-energy localized states on step edges and line defects originate from topologically trivial Yu-Shiba-Rusinov states. In addition, zero-energy bound states are also observed for regions without surface defects. A combined spatial and magnetic field dependent analysis of the spin-resolved tunneling spectra in these regions reveals that this type of zero-energy states cannot be attributed to the presence of Majorana bound states. These findings emphasize the importance of spin-dependent studies of low-energy states for pursuing Majorana zero modes.
Majorana zero modes are named after the Italian physicist Ettore Majorana, who predicted particles that are their own antiparticles and mysteriously disappeared in 1938.