SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 44: Focus Session: Superconducting Nickelates I

TT 44.4: Hauptvortrag

Donnerstag, 30. März 2023, 11:15–11:45, HSZ 03

Infinite-layer nickelate thin films: From synthesis to spectroscopy — •Daniele Preziosi — Université de Strasbourg, CNRS, IPCMS UMR 7504, F-67034 Strasbourg, France

In the last three decades, special efforts were devoted to the realization of nickelates mimicking the electronic structure of cuprates. These efforts led to the realization of infinite-layer nickelates characterized by a stable Ni−3d⁹ configuration and reduced dimensionality. A superconducting state below 15 K was reported for Nd_0.8Sr_0.2NiO₂ thin films deposited onto (001) SrTiO₃ (STO). Soon after this discovery, x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) experiments on undoped (LaNiO₂, NdNiO₂) and doped (Nd_1−xSr_xNiO₂) samples showed that infinite-layer nickelates show some important differences compared to layered cuprates, in particular a larger charge transfer energy and an important Nd 5d-Ni 3d hybridization. In this talk, after introducing our efforts to stabilize the infinite-layer phase, I will show that some of those aforementioned differences depend also on the presence/absence of a STO-capping-layer. A robust charge order is observed in undoped capping-free thin films, while strong magnetic excitations around 200 meV energy-loss characterize capped samples. Polarization-resolved RIXS measurements unambiguously demonstrated that also the low-energy excitations for uncapped samples are magnetic in nature, but largely damped. The ’altered’ doping effect as observed from the enlarging of the XAS feature at the Ni L₃-edge combined to a strong Ni 3d−Nd 5d hybridization for uncapped samples, may speak in favor of this extra softening.