In recent research published in Nature Physics, academician Xianhui Chen and Professor Ziji Xiang, leading a research team from the CAS Key Laboratory of Strongly-Coupled Quantum Matter Physics and the Department of Physics at the University of Science and Technology of China, unveiled a distinctive superconducting phenomenon. They identified one-dimensional superconducting stripes triggered by the ferromagnetic proximity effect within an oxide heterostructure. This structure consisted of ferromagnetic EuO and (110)-oriented KTaO3 (KTO).
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The consensus within the academic community is that unconventional superconducting pairings are closely associated with magnetism, especially in high-temperature superconductors like copper oxides and iron-based compounds.
Magnetic fluctuations are considered crucial to the development of high-temperature superconductivity, where the interaction between superconductivity and magnetism results in superconducting states with distinctive spatial modulation. Superconducting oxide heterostructures that include magnetic structural units are seen as an ideal platform for studying these superconducting states.
Building on their previous successes, the research team further investigated the superconductivity of this system and its relationship with the ferromagnetic proximity effect. They carefully adjusted the carrier concentration of the two-dimensional electron gas at the interface, discovering an intriguing in-plane anisotropy in superconductivity in samples with low carrier concentrations. This anisotropy, however, disappeared in samples with higher carrier concentrations.
The transition temperature of superconductivity, which varies with the current direction at the heterojunction interface, is attributed to the formation of one-dimensional superconducting stripes, a result of the reduced dimensionality of superconductivity. Additionally, the anomalous Hall effect and magnetoresistance hysteresis behavior suggest that the coupling between interfacial conduction electrons and ferromagnetism is influenced by band filling.
The hybridization of Eu and Ta atomic orbitals within a certain energy range leads to band spin splitting, aligning with the experimental results. This confirms that the one-dimensional superconducting stripes in the EuO/KTO(110) heterojunction are due to the coupling effect between superconductivity and magnetism.
This study unveils the existence of a superconducting stripe phase at the EuO/KTO(110) interface, induced by the ferromagnetic proximity effect. It provides the first clear experimental evidence of exotic superconducting states emerging from the intricate coupling between superconductivity and magnetism at oxide interfaces.
Journal Reference:
Hua, X., et al. (2024) Superconducting stripes induced by ferromagnetic proximity in an oxide heterostructure. Nature Physics. doi.org/10.1038/s41567-024-02443-x.