Observation of Half-Quantum Vorticity in an Iron-based Superconductor

TL;DR

This study provides direct transport evidence of half-quantum vortices in an iron-based superconductor with helical Dirac surface states, revealing fractional flux quantization and potential for topological quantum computing.

Contribution

It reports the first direct observation of half-quantum vorticity in an iron-based superconductor, demonstrating fractional flux quantization in mesoscopic devices.

Findings

Observation of half-integer quantum oscillations

Detection of trapped half-integer fluxoids

Modulation of oscillations by spin-orbit coupling

Abstract

Half-quantum vortices -- topological excitations carrying half the superconducting flux quantum -- are predicted to emerge in spin-triplet superconductors, where the spin component of order parameter enables fractional flux quantization. We present direct transport signatures of half-quantum vorticity in single-crystal Fe(Te,Se), an iron-based superconductor with helical Dirac surface states. Using mesoscopic superconducting ring devices, we observe half-integer quantum oscillations arising from the splitting of quantized fluxoid states, further supported by distinct signatures of trapped half-integer fluxoids. The quantum oscillations are modulated by a background symmetry, set by the relative orientation of the DC bias current and perpendicular magnetic field, consistent with strong spin-orbit coupling. These findings demonstrate the long-sought half-quantum vorticity in spin-polarized superconductors and open new directions toward non-Abelian excitations in quantum materials and scalable topological qubits.