New preprint: Switchable half-quantum flux states in a ring of the kagome superconductor CsV3Sb5
Our preprint Switchable half-quantum flux states in a ring of the kagome superconductor CsV3Sb5 was posted to arXiv on December 10, 2025. By turning high-quality kagome crystals into mesoscopic superconducting rings, the study establishes a phase-sensitive transport probe of unconventional superconductivity.
Why this matters
In a conventional superconducting ring, the Little-Parks effect is periodic in the standard superconducting flux quantum h/2e. A shift by half a flux quantum is a direct indication that the superconducting wave function accumulates an additional phase around the ring. Such measurements therefore provide information about pairing symmetry that cannot be obtained from the transition temperature alone.
Key findings
At low bias, the CsV3Sb5 rings show π-shifted Little-Parks oscillations, with the extrema displaced by half a superconducting flux quantum. The effect is highly reproducible: 12 of the 13 measured devices display the intrinsic π-shifted response. This device-to-device consistency is important for excluding accidental flux trapping or effects specific to a single device’s geometry.
A bias current reversibly switches the oscillations from the π-shifted state to the conventional state. In the intermediate regime, the oscillation period becomes h/4e. The continuous evolution between these regimes indicates competition and coexistence between distinct superconducting components, creating a controllable route to fractional-flux states in a solid-state device.
Collaboration and outlook
Professor Mark H. Fischer’s group at the University of Zurich and Professor Emeritus Manfred Sigrist’s group at ETH Zurich developed the theoretical framework for the competing superconducting components. Prof. Andreas Schnyder, Prof. Kam Tuen Law, Dr. Andras Szabo, and Dr. Xilin Feng also contributed to the theoretical framework. We also thank the collaboration from Prof. Ning Kang, Prof. Xiaosong Wu, Prof. Xuewen Fu and valuable discussions with Prof. Tao Wu and Prof. Hongming Weng.
Beyond the first phase-sensitive evidence of unconventional superconductivity in kagome superconductors, the ability to switch flux states electrically suggests new ways to investigate multicomponent pairing and may ultimately inform superconducting circuits in which phase and flux are active, controllable degrees of freedom.