Charge stripes strengthen around vortex cores in a cobalt-doped iron superconductor

A vortex is how a magnetic field gets into a type-II superconductor. Each one carries a fixed amount of magnetic flux, with electrical currents circulating around its centre ^[10]. "Magnetic vortices are particularly interesting because their cores provide a natural platform for exploring emergent electronic states in these unconventional superconductors," said Can-Li Song, the paper's senior author ^[9][15].

One state a vortex core can host is a Majorana zero mode. It is a localized, zero-energy electronic excitation that behaves as a particle that is its own antiparticle ^[11]. Phys.org notes that such states could be useful in quantum computing, because information stored across separated Majorana modes could be protected against some local disturbances ^[11].

The experiment compares many vortices. In spectroscopic imaging, an extremely fine tip moves just above the surface and maps the electronic states at different energies ^[7]. The same instrument therefore records both the stripe pattern and the spectrum at each vortex centre. "By mapping the electronic states around many vortices with atomic-scale precision, we identified charge stripes and two distinct types of vortex states, including those hosting Majorana zero modes, and revealed their intimate spatial correlation," said Yu Liu, the first author ^[12][15].

"Intimate spatial correlation" is the precise claim. A vortex is assigned to one type or the other by where its centre falls on the stripes, and the zero-energy state appears in one type only ^[5]. Separately, the stripes grow stronger close to the cores ^[3]. The first observation fits a story in which the stripes help set where a Majorana-hosting vortex can sit. The second fits a story in which the vortex reshapes the charge order around it. Both could also follow from a third ingredient, such as the possible pair-density modulation that co-author Xu-Cun Ma described ^[13][15]. As reported, the maps do not separate these.

How strict the sorting is depends on counts the Phys.org account does not report: how many vortices were mapped, what share fell into each type, and the field and temperature of the measurements.

The zero-energy state's label also comes from the authors. The researchers identified it as a Majorana zero mode ^[5], and the account gives the identification without describing the tests behind it.

Ma's own summary is broad. "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," he said ^[13]. "This reveals how topology, charge order, and superconductivity can interact at the nanoscale," he added ^[14]. I think "can interact" is the right verb for what was shown. The films are of a single compound, Ba(Fe0.94Co0.06)2As2, with cobalt on 6% of the iron sites ^[4].