Flux quantum fractionalization and unquantized vortices in superconductors

Date

Oct 27, 2026

Time

10:00 AM - 11:00 AM

Speaker

Dr. Vadim Grinenko

Affiliation

Shanghai Jiao Tong University

Language

en

Main Topic

Materialien

Host

Rita Taubert

Description

Magnetic flux quantization is a defining hallmark of superconductivity, traditionally constraining vortices to carry integer multiples of the flux quantum Φ₀. Recent advances in multiband superconductors challenge this paradigm by demonstrating the emergence of vortices carrying fractional, continuously tunable flux [1-3]. Here, we overview recent experimental breakthroughs to present a unified picture of vortex deconfinement, and emergent composite excitations in multicomponent superconducting systems. Three years ago, scanning SQUID magnetometry in Ba₁₋ₓKₓFe₂As₂ revealed mobile vortices carrying a nonuniversal, temperature-dependent fraction of Φ₀, demonstrating that flux quantisation can be continuously violated in multiband systems [1]. Complementary spectroscopic imaging via scanning tunnelling microscopy further shows that integer vortices can split into multiple fractional core singularities, establishing a direct link between multiband phase structure and vortex-core fractionalization [2]. These findings are consistent with theoretical predictions that multicomponent superconducting condensate can support phase windings in the individual components of the order parameter [4,5]. Extending these observations, recent scanning SQUID magnetometry visualized the real-space deconfinement of integer flux vortices: integer vortices can spontaneously split into spatially separated, yet correlated, fractional-flux objects stabilized by pinning and thermal fluctuations [3]. Notably, the flux of these constituents exhibits an anticorrelated temperature dependence while conserving the total flux, forming a “see-saw” redistribution mechanism. This behavior reveals a striking analogy to quark confinement and deconfinement, where fractional vortices act as linearly interacting constituents of composite topological objects. Together, these studies establish fractional flux unquantized vortices as robust, mobile, and tunable excitations in multiband superconductors. Their existence expands the fundamental understanding of topological defects beyond conventional quantization arguments and opens new avenues for engineering novel fluxonics devices. Moreover, the stability of unquantized vortices establishes them as candidates for observing anyons, which may be represented, as shown by Frank Wilczek [6], as an integer charge bound to a fractional flux tube. These results position multicomponent superconductors as a promising platform for exploring emergent topology and fractionalized quantum matter. Bibliography 1. Y. Iguchi, et al. Science, 380(6651), 1244–1247 (2023). 2. Y. Zheng, et al. Science 393, 80-84 (2026). 3. Q. Z. Zhou et al. arXiv:2408.05902 (2024). 4. E. Babaev, Model. Phys. Rev. Lett. 89, 067001(2002). 5. I. Timoshuk and E. Babaev, New J. Phys. 27 (2025) 123501. 6. F. Wilczek, Phys. Rev. Lett. 48, 1144–1146 (1982).

Links

• Seminars at the IFW

Last modified: Oct 27, 2026, 7:40:01 AM