Tuning interface sharpness and interface superconductivity at La₂CuO₄ heterostructures

Abstract text (incl. figure legends and references)

Heterostructures of transition-metal oxides enable emerging unique physical properties at their interfaces [1]. The structural adaptability of La₂CuO₄ allows for designing different heterostructures, and superconductivity takes place at the interface between overdoped (metallic) and undoped (insulating) La₂CuO₄ layers grown by oxide molecular beam epitaxy (MBE)[2]. In addition to homo-epitaxial systems[3], heterogeneous multilayers of La₂CuO₄ with, for example, perovskite 113-type and 214-type lanthanum nickelate layers revealed the impact of the interface sharpness on thermoelectric and superconducting properties, respectively [4,5].

In this work, we fabricate (La,Sr)₂CuO₄–SrMnO_3­–LaMnO₃–La2CuO₄ superlattices [6] using oxide MBE and focus on the interface sharpness and the related superconducting mechanism compared to cuprate–cuprate interfaces. We use scanning transmission electron microscopy (STEM) techniques, including high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging, electron energy-loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDXS) to examine the interfaces. A JEOL JEM-ARM200F STEM equipped with a cold field-emission electron source, a probe Cs-corrector (DCOR, CEOS GmbH), a Gatan GIF Quantum ERS spectrometer and a large solid-angle JEOL Centurio SDD-type EDXS detector was used for atomic-resolution analyses.

Our findings demonstrate that hetero-epitaxial cuprate–manganite layers can achieve sharper Sr-doped La₂CuO₄ interfaces. The dopant distribution in La₂CuO₄ is affected by the elemental intermixing in the first atomic LaMnO₃ monolayer. We further underline that structurally sharp interfaces can be chemically rough (Fig. 1), and the chemical intermixing dominates the physical properties. Importantly, different superconducting behaviour (e.g., interface vs filamentary) can be customized with interfacial design [7].

References

[1] Y. E. Suyolcu, G. Christiani, P. A. van Aken, G. Logvenov, J. Supercond. Nov. Magn. 2020, 33, 107.

[2] A. Gozar, G. Logvenov, L. F. Kourkoutis, A. T. Bollinger, L. A. Giannuzzi, D. A. Muller, I. Bozovic, Nature 2008, 455, 782.

[3] Y. E. Suyolcu, Y. Wang, F. Baiutti, A. Al-Temimy, G. Gregori, G. Cristiani, W. Sigle, J. Maier, P. A. van Aken, G. Logvenov, Sci. Rep. 2017, 7, 453.

[4] F. Baiutti, G. Gregori, Y. E. Suyolcu, Y. Wang, G. Cristiani, W. Sigle, P. A. van Aken, G. Logvenov, J. Maier, Nanoscale 2018, 10, 8712.

[5] P. Kaya, G. Gregori, F. Baiutti, P. Yordanov, Y. E. Suyolcu, G. Cristiani, F. Wrobel, E. Benckiser, B. Keimer, P. A. van Aken, H.-U. Habermeier, G. Logvenov, J. Maier, ACS Appl. Mater. Interfaces 2018.

[6] G. Kim, Y. Khaydukov, M. Bluschke, Y. E. Suyolcu, G. Christiani, K. Son, C. Dietl, T. Keller, E. Weschke, P. A. van Aken, G. Logvenov, B. Keimer, Phys. Rev. Mater. 2019, 3, 084420.

[7] This work has received funding the European Union's Horizon 2020 research and innovation programme under grant agreement No. 823717 – ESTEEM3.

Figure 1. (a) STEM-HAADF image of a La₂CuO₄–SrMnO₃–LaMnO₃–La₂CuO₄ superlattice demonstrating coherent "A" and "B" interfaces. (b) EDX line-scan profiles reveal Cu (red) and Mn (green) intermixing at the interfaces. Sr (orange) and La (blue) profiles are given as guides indicating the individual layers. The blue arrow depicts the region of the acquired EDX line scan profiles.