Links between La N4,5-edge RIXS probed A-site covalency, structural parameters and superconducting properties in optimally doped La1.84M0.16CuO4 (M = Ca, Sr, Ba) epitaxial films and the La2CuO4 host lattice
Abstract
We investigate La-site bonding by La N 4,5 -edge RIXS together with structural parameters and the superconducting transition temperature Tc of optimally doped La 1.84 M 0.16 CuO 4 (M = Ca, Sr, Ba) epitaxial films and the La 2 CuO 4 host lattice. La and M in the A-site have been considered to be part of the axial hybrid state formed by Cu 4 s , apical O 2 pz , and rare earth (La) states. In La 2−x M x CuO 4 (M = Ca, Sr, Ba) these states have been proposed as contributing to the superconducting transition temperature Tc . We observe a systematic decrease of the La 5p54f1 3D1 RIXS energy loss across the Ca–Sr–Ba doped film series. Based on previous La N 4,5 -edge RIXS studies, this trend is consistent with a La-site response to enhanced hybridization and local screening. The trend follows increasing A-site ionic radius and c -axis expansion, but these quantities are coupled to tetragonal distortion, unit-cell volume, epitaxial strain, relaxation, and possible symmetry changes. The undoped LCO host lattice shows a La 3D1 energy close to the Sr-doped film, suggesting that its La-site environment cannot be described by ionic radius alone. However, because the LCO film differs in thickness and relaxation state from the doped films, this comparison is treated as qualitative. The superconducting transition temperature does not follow the La 3D1 trend monotonically: the Sr-doped film has the highest Tc , whereas the Ba-doped film shows a reduced Tc despite the lowest 3D1 energy loss. This indicates that the local A-site bonding response probed by La N 4,5 -edge RIXS is only one contribution among broader structural and electronic effects.
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BibTeX
@article{kusch2026links,
title = {{Links between La $$N_4,5$$-edge RIXS probed A-site covalency, structural parameters and superconducting properties in optimally doped La$$_1.84$$M$$_0.16$$CuO$$_4$$ (M = Ca, Sr, Ba) epitaxial films and the La$$_2$$CuO$$_4$$ host lattice}},
author = {Maximilian Kusch and Katarzyna Estera Siewierska and Chun Yu Liu and Marco Kliem and Kari Ruotsalainen and Régis Decker and René Schwiddessen and Gennady Logvenov and Georg Christiani and Eva Benckiser and Daniele Di Castro and Alexander Föhlisch},
journal = {Scientific Reports},
year = {2026},
month = oct,
doi = {10.1038/s41598-026-74863-z},
url = {https://www.nature.com/articles/s41598-026-74863-z},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Links between La N_4,5-edge RIXS probed A-site covalency, structural parameters and superconducting properties in optimally doped La_1.84M_0.16CuO_4 (M = Ca, Sr, Ba) epitaxial films and the La_2CuO_4 host lattice
AU - Maximilian Kusch
AU - Katarzyna Estera Siewierska
AU - Chun Yu Liu
AU - Marco Kliem
AU - Kari Ruotsalainen
AU - Régis Decker
AU - René Schwiddessen
AU - Gennady Logvenov
AU - Georg Christiani
AU - Eva Benckiser
AU - Daniele Di Castro
AU - Alexander Föhlisch
PY - 2026
DA - 2026/10/15
JO - Scientific Reports
DO - 10.1038/s41598-026-74863-z
UR - https://www.nature.com/articles/s41598-026-74863-z
AB - We investigate La-site bonding by La N _4,5 -edge RIXS together with structural parameters and the superconducting transition temperature T_c of optimally doped La _1.84 M _0.16 CuO _4 (M = Ca, Sr, Ba) epitaxial films and the La _2 CuO _4 host lattice. La and M in the A-site have been considered to be part of the axial hybrid state formed by Cu 4 s , apical O 2 p_z , and rare earth (La) states. In La _2−x M _x CuO _4 (M = Ca, Sr, Ba) these states have been proposed as contributing to the superconducting transition temperature T_c . We observe a systematic decrease of the La 5p^54f^1 ^3D_1 RIXS energy loss across the Ca–Sr–Ba doped film series. Based on previous La N _4,5 -edge RIXS studies, this trend is consistent with a La-site response to enhanced hybridization and local screening. The trend follows increasing A-site ionic radius and c -axis expansion, but these quantities are coupled to tetragonal distortion, unit-cell volume, epitaxial strain, relaxation, and possible symmetry changes. The undoped LCO host lattice shows a La ^3D_1 energy close to the Sr-doped film, suggesting that its La-site environment cannot be described by ionic radius alone. However, because the LCO film differs in thickness and relaxation state from the doped films, this comparison is treated as qualitative. The superconducting transition temperature does not follow the La ^3D_1 trend monotonically: the Sr-doped film has the highest T_c , whereas the Ba-doped film shows a reduced T_c despite the lowest ^3D_1 energy loss. This indicates that the local A-site bonding response probed by La N _4,5 -edge RIXS is only one contribution among broader structural and electronic effects.
SN - 2045-2322
ER -