Topological superconductors are predicted to host Majorana fermions — quasiparticles that are their own antiparticles — on their surfaces. These Majorana modes are protected by topology: they cannot be removed by smooth deformations of the Hamiltonian, making them candidates for fault-tolerant quantum computing. But most proposed topological superconductors are engineered — semiconductor nanowires coupled to conventional superconductors, with magnetic fields tuned to create the topological state. The topological superconductivity is extrinsic: it requires careful assembly of non-superconducting components.
Srivastava, Samanta, Meena, and collaborators (arXiv 2602.22793, February 2026) identify TaPtSi as an intrinsic topological superconductor — a material that superconducts on its own and hosts topological surface states without external engineering.
The mechanism relies on the crystal's nonsymmorphic symmetry. Nonsymmorphic space groups contain symmetry operations that combine point-group transformations with fractional translations — glide planes and screw axes that have no fixed point. These symmetries enforce band crossings that cannot be gapped: hourglass dispersions, where bands cross in an X-shaped pattern, and Dirac nodal rings, where band crossings form closed loops in momentum space. The crossings are topologically protected by the nonsymmorphic symmetry itself.
TaPtSi belongs to such a space group. Its normal-state electronic structure features hourglass Dirac chains — connected networks of nodal crossings that thread through the Brillouin zone. When the material enters the superconducting state below its critical temperature, the topological character of these normal-state bands imprints on the superconducting state. The pairing symmetry is unconventional: muon spin rotation experiments detect spontaneous time-reversal symmetry breaking below the superconducting transition, indicating triplet pairing with a complex order parameter. The combination of topological normal-state bands and triplet pairing produces Majorana surface modes.
The evidence is multi-probe. AC transport and magnetization measurements establish the superconducting phase diagram. Heat capacity shows the thermodynamic signatures. Muon spin rotation provides the crucial evidence of time-reversal symmetry breaking — an internal magnetic field that appears only below the superconducting transition temperature, which is impossible for a conventional singlet superconductor and indicates the complex triplet order parameter that the topological classification requires.
The material is a ternary silicide — tantalum, platinum, silicon — synthesized by standard solid-state chemistry methods. It is not a nanowire, not a heterostructure, not a device. It is a bulk crystal that happens to have the right symmetry (nonsymmorphic, enforcing topological band crossings) and the right pairing (triplet, enabling Majorana modes). The topological superconductivity was not designed. It was discovered by checking the symmetry, measuring the pairing, and finding that the material already satisfies both requirements.