Vortex pinning of Ba$_{0.62}$K$_{0.38}$BiO$_3$ investigated by magneto-optical Kerr-effect and magnetization measurements

Soichiro Yamane; Sota Nakamura; Atsutoshi Ikeda; Dayu Zhai; Siddarth Gorregattu; Xing He; Sudarshan Sharma; Yipeng Cai; Yasutomo J. Uemura; Martin Greven; Shingo Yonezawa

arXiv · 2606.10300

Vortex pinning of Ba$_{0.62}$K$_{0.38}$BiO$_3$ investigated by magneto-optical Kerr-effect and magnetization measurements

Soichiro Yamane·Sota Nakamura·Atsutoshi Ikeda·Dayu Zhai·Siddarth Gorregattu·Xing He·Sudarshan Sharma·Yipeng Cai·Yasutomo J. Uemura·Martin Greven·Shingo Yonezawa

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Abstract

Vortex pinning plays a crucial role in determining properties of type-II superconductors. For example, it governs the irreversible magnetic response as well as dissipation caused by vortex motion. Here, we study vortex pinning in the three-dimensional oxide superconductor Ba1-xKxBiO3 using ultra-high-resolution magneto-optical Kerr effect (MOKE) and detailed magnetization measurements. We find that the zero-field MOKE signal in the superconducting state exhibits a pronounced magnetic-history dependence. This behavior closely resembles the remanent magnetization caused by trapped vortices. Furthermore, we demonstrate that the observed evolution of the MOKE signals is well described by Bean's critical-state model for trapped vortices. Our results establish MOKE as a viable optical and mesoscopic probe of vortex pinning in type-II superconductors, providing a new complementary approach to investigate mixed-state phenomena. We also find that the training-field dependence of the MOKE is linear near zero training field, without any anomalies indicative of spontaneous time-reversal-symmetry breaking in an unconventional superconducting state. Our study defines a clear protocol to distinguish vortex-induced MOKE responses from those associated with a time-reversal-symmetry broken superconducting order parameter.

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Soichiro Yamane, Sota Nakamura, Atsutoshi Ikeda, Dayu Zhai, Siddarth Gorregattu, Xing He, Sudarshan Sharma, Yipeng Cai, Yasutomo J. Uemura, Martin Greven, Shingo Yonezawa. 2026-06-09. Vortex pinning of Ba$_{0.62}$K$_{0.38}$BiO$_3$ investigated by magneto-optical Kerr-effect and magnetization measurements. https://arxiv.org/abs/2606.10300

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