Physicists Spot Majorana Zero Modes Inside Magnetic Vortices of an Iron-Based Superconductor, Tangled With Charge Stripes
Tsinghua-led scanning-tunneling images show electronic stripes growing stronger at vortex cores, with one of two vortex types hosting the exotic particle that is its own antiparticle.
Superconductors, materials that carry electric current with zero resistance, have proved promising for medical devices, particle accelerators and quantum computers. Studying them can also uncover new physical states with potential uses. A team at Tsinghua University, the Southern University of Science and Technology, Boston College and other institutions has now reported a surprising link between electronic stripes and exotic states trapped inside magnetic vortices in an iron-based superconductor. The paper appeared in Physical Review Letters.
Some superconductors, known as type-II, let magnetic fields in through tiny regions called vortices. Each vortex carries a fixed amount of magnetic flux, with electrical currents circulating around its center. The researchers examined electronic states bound near vortex centers in thin films of cobalt-doped barium iron arsenide, Ba(Fe0.94Co0.06)2As2, in which cobalt replaces 6% of the iron.
The team grew the films by molecular beam epitaxy and studied them with low-temperature scanning tunneling microscopy and spectroscopy. The technique moves an extremely fine tip just above a surface to map electronic properties at different energies. "Our initial goal was to search for vortex bound states and possible Majorana zero modes in 122-type iron pnictides," said senior author Can-Li Song. "Unexpectedly, we discovered charge stripes closely intertwined with different vortex states."
The stripes are periodic modulations of electronic charge along one direction, and they became stronger around vortex centers. By mapping the states around many vortices with atomic-scale precision, the researchers distinguished two types of vortex according to where their centers sit relative to the stripe pattern. One type hosted a zero-energy state that the team identified as a Majorana zero mode.
A Majorana zero mode is a localized, zero-energy collective excitation that behaves like a particle that is its own antiparticle. It matters for quantum computing because information stored across separated Majorana modes could be protected against some local disturbances. That promise has driven years of searching for such modes in superconductors.
"The most exciting finding is that a Majorana zero mode, charge stripes, and a possible pair-density modulation all emerge within a single magnetic vortex and are intimately intertwined," said co-author Xu-Cun Ma. "This reveals how topology, charge order, and superconductivity can interact at the nanoscale." First author Yu Liu said the work grew from a long-term effort to understand high-temperature superconductivity with atomic precision, since vortex cores offer a natural platform for emergent electronic states.
The result shows that electronic stripes and states bound at magnetic vortices are related in this specific material. Other research groups could now test whether the same relationship holds in other type-II superconductors, which would show whether it is a general feature or a quirk of this compound.
Song said the team wants to understand why the stripes select different types of vortices, how they couple to Majorana states, and whether the intertwined behavior is universal across iron-based superconductors. "Ultimately," he said, the goal is to learn how these interactions can be used to control and manipulate Majorana zero modes. The study is also posted on arXiv and carries the DOI 10.1103/6f1z-dvc6.
