Tinkering with Superconductivity in a Quasicrystal
A quasicrystal isn’t an obvious home for superconductivity. Conventional theory says that pairs of electrons with opposite momenta are needed for superconductivity, and electron momentum is hard to define in a quasicrystal—a material without long-range periodicity. But in 2018, experimentalists saw the resistance of a quasicrystalline alloy drop to zero—a signature of superconductivity that invited models to describe the unexpected behavior. Using a toy model, researchers now describe how a quasicrystal superconductor responds to a magnetic field and find that the field induces an exotic type of superconductivity that is spatially nonuniform.
Shiro Sakai and Ryotaro Arita of RIKEN in Japan consider a plane of about 11,000 atoms arranged in a Penrose tiling—one of the simplest quasicrystalline lattices. The team previously predicted superconductivity for this lattice by adapting a simple “Hubbard” model for conventional superconductors. In their new work, they extend the model to include a magnetic field that interacts with the electrons. For a range of field-strength values, they calculate a fundamental parameter of superconductivity—the energy gap—at each point in the lattice.
Sakai and Arita find that when the field strength exceeds a certain value, superconductivity dies, just as in periodic materials. But they also found a range of fields and temperatures where the gap varies in value and sign from point to point in the lattice. This variation is reminiscent of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase—a spatially inhomogeneous superconductor with a mixture of paired and unpaired electrons. The researchers say quasicrystals may be a new platform for studying the FFLO phase, which has proven tough to see in experiments.
This research is published in Physical Review Research.
Jessica Thomas is the Editor of Physics.