Doping evolution of spin excitations in La$_{3-x}$Sr$_{x}$Ni$_2$O$_7$/SrLaAlO$_4$ superconducting thin films

TL;DR

This study investigates how spin excitations evolve with doping in La$_{3-x}$Sr$_x$Ni$_2$O$_7$ thin films, revealing a strong link between magnetic coherence and superconductivity through spectroscopic measurements.

Contribution

It provides the first detailed doping-dependent analysis of spin excitations in bilayer nickelate films using RIXS, highlighting the collapse of magnetic coherence at high doping levels.

Findings

Dispersive spin excitations persist in superconducting regime.

Magnetic response becomes broadened and weakened at high doping.

Magnetism and superconductivity are directly linked through doping.

Abstract

Ambient-pressure superconductivity in compressively strained bilayer nickelate films enables direct spectroscopic tests of pairing scenarios, yet how magnetism evolves with carrier doping remains largely unexplored. Here we use Ni $L_3$-edge resonant inelastic x-ray scattering (RIXS) to track electronic and spin excitations in coherently strained La$_{3-x}$Sr$_x$Ni$_2$O$_7$/SrLaAlO$_4$ thin films ($x=0$, $0.09$, $0.21$ and $0.38$), spanning superconducting and overdoped non-superconducting regimes at essentially fixed epitaxial strain. Transport confirms superconductivity for $x\le0.21$ and a weakly insulating normal state at $x=0.38$. The $dd$-excitation manifold evolves weakly up to $x=0.21$, whereas the $\sim0.4$ eV and $\sim1.6$ eV features broaden and lose intensity at $x=0.38$. In the superconducting films, dispersive spin excitations persist along both $[H, H]$ and $[H, 0]$ with nearly doping-independent undamped dispersions and only a modest reduction of spectral weight, consistent with robust double-stripe correlations. By contrast, at $x=0.38$ the magnetic response becomes strongly broadened and weakened, with enhanced damping and $\sim50\%$ lower spectral weight, indicating a collapse of coherent double-stripe spin excitations. The concomitant suppression of magnetic coherence and superconductivity establishes a direct doping-controlled link between magnetism and superconductivity in bilayer nickelate films.