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In a single crystal of multiband superconductors, it is theoretically expected that the quantum phase winding around an isolated vortex is only in one of the bands at the level of Ginzburg-Landau theory. This one-band phase winding induces unquantized vortices, whose total flux may be a part of the flux quantum and temperature-dependent. However, this vortex type had never been observed experimentally since its first theoretical discovery in 2002.
We investigate isolated vortices in the multiband superconductor Ba1-xKxFe2As2(x=0.77) by using scanning superconducting quantum interference device (SQUID) magnetometry [1]. In many locations, we observed vortices that carried only part of a flux quantum, with a magnitude that varied continuously with temperature. We interpret these features as vortices with unquantized magnetic flux, whose magnitude is determined by the temperature-dependent parameters of a multiband superconductor. We further characterize the mobility and manipulability of the unquantized vortices.
[1] Y. Iguchi, R. A. Shi, K. Kihou, C.-H. Lee, M. Barkman, A. L. Benfenati, V. Grinenko, E. Babaev, and K. A. Moler, Superconducting vortices carrying a temperature-dependent fraction of the flux quantum, Science 380, 1244-1247 (2023). (Open access link available here)
Dr. Iguchi received his B.S. in physics at Tokyo University of Science in 2013 and received his Ph.D. in Basic Science from the University of Tokyo in 2018. He was JSPS Overseas Fellow in Applied Physics at Stanford University during 2018-2020. He then joined the Geballe Laboratory for Advanced Materials at Stanford University as a senior research scientist. Since 2018, he has worked in Prof. Kathryn Ann Moler’s group.
Dr. Iguchi is an experimental physicist at the forefront of condensed matter physics, with a focus on unconventional superconductors and non-centrosymmetric magnets. His wide-ranging research covers diverse areas, including the exploration of spin dynamics in ferromagnetic insulators and chiral edge currents in topological superconductors. His achievements include the observation of non-reciprocal magnon-propagation in chiral ferromagnets, pioneering electromagnetic control over non-reciprocal microwave propagation in multiferroic materials, uncovering local superconducting states and intrinsic magnetism in candidates for chiral superconductors, and the observation of unquantized vortices in multiband superconductors.
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