Séminaire – Abhishek Ranna
Le vendredi 16 septembre à 11h (auditorium TRT), nous aurons le plaisir d’accueillir Abishek Ranna (Max Planck Institute for Chemical Physics of Solids, Dresden) qui présentera un séminaire au laboratoire.
Titre:
“Infinite-Layer Nickelates: Superconductivity and Electronic Transport Under Controlled Introduction of Disorder”
Abstract:
The discovery of superconductivity in thin films of hole-doped infinite-layer (Nd,Sr)NiO2 introduced a new family of oxide superconductors. Initially proposed as cuprate analogues because of their square-planar structure and nominal 3d9 Ni electron configuration, these materials also exhibit differences in their electronic structure and hybridization [1]. Since then, superconductivity has been realized across several rare-earth and dopant combinations, including the formally undoped parent compounds. Advances in synthesis and reduction methods have raised superconducting transition temperatures to 35 K in Sm(Eu,Ca,Sr)NiO2 thin films [2]. These developments raise questions about the superconducting pairing symmetry and the roles of rare-earth composition and doping in their superconducting and normal-state properties.
Determining the superconducting gap symmetry remains experimentally challenging because the thin film geometry and surface degradation associated with chemical reduction limit the applicability of conventional probes such as single particle tunnelling [5] and photoemission spectroscopy [3,4]. High-energy electron irradiation provides an alternative approach by introducing controlled point disorder and tracking its effects on superconductivity. Measurements on Nd-based nickelates reveal a progressive suppression of the superconducting transition temperature and an increase in normal-state resistivity, supporting a sign-changing superconducting order parameter [6]. Extensions to Nd-, Pr-, and La-based films and different Sr concentrations examine how the response to disorder depends on rare-earth composition and doping.
The seminar will discuss these results alongside the evolution of normal-state transport with irradiation. This approach helps distinguish intrinsic electronic behaviour from variations associated with synthesis, with broader implications for understanding nickelates and related oxide superconductors.
References
[1] Wang, Lee & Goodge. Annu. Rev. Condens. Matter Phys. 15:53, 305 (2024).
[2] Chow et al. Nature 642, 8–63 (2025). [3] Sun et al. Science Advances 11, eadr5116 (2025).
[4] Ding et al. National Science Review 11, nwae194 (2024).
[5] Gu et al. Nature Communications 11, 6027 (2020).
[6] Ranna et al. Phys. Rev. Lett. 135, 126501 (2025).
