The researchers, from the Indian Institute of Science Education and Research Bhopal, the Indian Institute of Technology Kanpur, and ISIS, found that the compounds combined conventional bulk type-II superconductivity with unusual surface states that could give rise to topological superconductivity. Materials with this combination of properties could form the basis of next-generation quantum computers and nanoscale electronic devices.
Topological superconductors could potentially be used to create more robust quantum computers as researchers can encode information in these materials in the form of quasiparticles called Majorana zero modes. These quasiparticles can serve as qubits, the basic unit of information in a quantum computer. As these quasiparticles are a feature of the material's topological order, they are more stable and less error-prone than typical quantum computers that rely on trapped ions or photons.
However, researchers have found that topological superconductors with the ideal properties for use in quantum computing are very rare.
In this study, the researchers were interested in ternary germanides MIrGe, where M is either Ti or Hf. They belong to a group of compounds that show a wide range of superconducting behaviours, although these precise compounds had not yet been thoroughly explored. Muons are particularly well suited to studying superconductors as they are highly sensitive to local magnetic fields.
Using a combination of resistivity, magnetization, and specific heat measurements they found that the MIrGe compounds show conventional bulk type-II superconductivity, with higher than usual transition temperatures for such superconductors. Zero field µSR on the MuSR instrument at ISIS revealed no magnetic field beneath the transition temperatures, indicating that the superconducting state preserves time reversal symmetry, and transverse field-µSR revealed an isotropic s-wave superconducting gap structure.
The team used first-principles calculations and symmetry analysis to show that the materials exhibited more unusual states on the surface. In particular, they found symmetry-protected hourglass topology and helical spin-textured surface states, leading to the potential for topological superconductivity at the surface.
“The interesting thing is that these materials show conventional bulk superconducting behaviour," says Rhea Stewart, ISIS instrument scientist and one of the paper's authors, “but in combination with a topological band structure. That's very exciting because it indicates the possibility for topological superconductivity at the surface of the materials, which is very rare."
The combination of superconductivity and the surface features will allow researchers to use these and similar compounds to study how topological features interact with superconductivity, which could be useful in developing robust quantum computing. The materials could also have applications in spintronics.
Related publication: Superconductivity in Hourglass Dirac Chain Metals (Ti, Hf)IrGe - Meena - Advanced Science - Wiley Online Library
