Significant Enhancement in Critical Current Density induced by Magnetic Field Cool Field process at high-Tc- superconductor/Oxide-Ferromagnet interface

Sagar Mal Kumawat^1,3*, G. D. Dwivedi¹, P.F. Su¹, W.S. Shyu¹, Y. H. Chien¹, S.P. Wei¹, N.D.B. Fernandez^1,2, C. H. Hsu⁴, S. Yang⁴, S. J. Sun², H. Chou^1,2

¹Department of Physics and Center for Crystal Research, National Sun Yat-sen University, Kaohsiung City, Taiwan
²Department of Applied Physics,, National University of Kaohsiung, Kaohsiung City, Taiwan
³International Ph.D. program for Science (IPPS), National Sun Yat-sen University, Kaohsiung City, Taiwan
⁴National Synchrotron Radiation Research Center, Hsinchu City, Taiwan

* Presenter:Sagar Mal Kumawat, email:kumawat123sagar@gmail.com

In this comprehensive study, the focus is on investigating interface effects within epitaxial tri-layer thin films consisting of a high-temperature superconductor (YBCO) and ferromagnetic layers (LSMO). To delve into the structural aspects, advanced X-ray techniques such as X-ray diffraction (XRD), X-ray reflectivity (XRR), and reciprocal space mapping (RSM) were employed. These techniques provided insights into the lattice constants of the films, both in the in-plane and out-of-plane orientations, shedding light on the precise arrangement of the atomic layers. Notably, the RSM analysis revealed a striking phenomenon in the LY15L films, where the YBCO (108) and LSMO (003) peaks split into two distinct peaks. However, the LY30L films displayed an intriguingly singular peak, suggesting a complex interplay at the interface of these layers. To corroborate the film structure, X-ray reflectivity patterns and transmission electron microscopy (TEM) scans were employed, confirming not only the thickness of each layer but also the presence of interlayers at the interface between LSMO and YBCO, further emphasizing the unique interface characteristics. The study also delved into the electrical properties of these tri-layer films. The resistance vs. temperature (RT) curve revealed the critical temperature (Tc) of YBCO, indicating a Tc of 60K for LY15L and 86K for LY30 L films. These critical temperatures signify the point at which the materials transition into a superconducting state, and they play a crucial role in the subsequent analyses. A particularly striking observation emerged from the current vs. voltage (I-V) scans conducted under the influence of an in-plane applied magnetic field at different Field Cooled Field (FCF) conditions. This study found a significant and unexpected enhancement in the critical current density (Jc) at the interface of the LSMO/YBCO/LSMO heterostructures. Remarkably, this enhancement was more pronounced in the LY30L films, where Jc increased by approximately 90% at an applied magnetic field of 0.6T, a phenomenon that had not been observed previously. This astonishing behaviour strongly suggests the potential existence of triplet superconducting pairs within the system and at the interface between the superconductor and the ferromagnetic layer, which is highly unconventional and opens up new avenues of exploration in the field of superconductivity. To explain this unusual enhancement in Jc, the study proposed phenomenological and combination models. These models are based on both singlet and triplet superconductivity mechanisms, which are fundamentally distinct forms of superconducting behaviour. The combination of these mechanisms may provide valuable insights into the underlying physics responsible for the enhancement in critical current at the interface of LSMO/YBCO/LSMO heterostructures.

Keywords: Interface Effect, Spin-Triplet Superconding cooper Pair , Superconductivity & Magnetism, Charges transfer from bulk to interface, Antiferromagnetic coupling between Mn and Cu moments