Source capture
Authors Martin Gonzalez, Andreas Suter, Michal Kiaba, Thomas Prokscha, Zaher Salman, Marc Gabay, Harold Y. Hwang, Jennifer Fowlie
arXiv / Publisher https://arxiv.org/abs/2609.03388
PDF https://arxiv.org/pdf/2609.03388
Relevance score 5.270
Primary category cond-mat.supr-con
Published 2026-09-04
Research paradigm Experimental
Sample form Thin Film

Summary

Using muon spin rotation/relaxation (μSR), this study systematically measured a series of infinite-layer nickelate (La,Sr)NiO2 samples spanning from the parent compound through the superconducting dome to the overdoped regime (Sr doping 0% ≤ x ≤ 25%) to probe the magnetic ground state and temperature-dependent static and dynamic magnetism. The results show that, regardless of doping level, local magnetic moments undergo spin freezing at temperatures on the order of tens of kelvin and enter a glassy state, and no anomaly is observed near the superconducting onset, indicating that the magnetism is intrinsic and essentially independent of hole concentration. With increasing hole doping, the glassy state shows only a weak tendency toward destabilization. These observations suggest that magnetism and superconductivity in nickelates are largely decoupled, and that their indirect interactions need to be understood within a multiorbital framework.

Materials

Methods

  • muon spin rotation/relaxation (μSR)
  • zero-field μSR
  • weak-transverse-field μSR
  • longitudinal-field μSR
  • PLD
  • topochemical reduction with CaH2
  • x-ray diffraction
  • temperature-dependent resistivity
  • Monte Carlo depth-profile simulations

Keywords

  • spin glass
  • glassy spin freezing
  • local moments
  • magnetic volume fraction
  • magnetism superconductivity decoupling
  • multi orbital framework
  • hole doping
  • superconducting dome
  • dynamic fluctuations
  • rkky interaction

Highlights

  • Local moments persist through the entire doping series, with all samples exhibiting a gradual crossover from a room-temperature paramagnetic regime into a low-temperature state with full magnetic volume fraction.
  • The observation of a fully magnetic phase across both non-superconducting and superconducting regimes confirms that local-moment magnetism is an intrinsic property of infinite-layer nickelates.
  • The persistence of a fully magnetic state stands in contrast with cuprates and iron pnictides, which exhibit suppression of magnetic volume fraction with increased doping.
  • No anomalies are observed at the onset of superconductivity, either upon cooling through the transition or upon hole-doping into or out of the superconducting dome.
  • Weak-transverse-field field-dependent measurements provide direct evidence of low-temperature glassy behavior, supported by longitudinal-field measurements showing slowing of dynamic fluctuations below 40 K.

Conclusions

  • Local moments experience spin freezing into a glassy state at temperatures on the order of a few tens of kelvin regardless of the doping level.
  • The nickelate samples reach a fully magnetic state across all doping levels at temperatures between 5 and 15 K.
  • The emergence of intrinsic local magnetic moments occurs regardless of the doping level, and no anomalies are observed at the superconducting transition temperature.
  • With increased hole doping, there is a subtle destabilization of the glassy state and an increase in fluctuation rate at 40 K.
  • Magnetism and superconductivity in infinite layer nickelates are largely decoupled phenomena with indirect interactions described in a multi-orbital framework.
  • Weak-transverse-field and longitudinal-field measurements support low-temperature glassy behavior and gradual spin freezing.

Main claims

  • Local electronic moments persist across the entire (La,Sr)NiO2 doping series and undergo spin freezing into a glassy state at temperatures on the order of tens of kelvin.
    • Evidence: For all doping levels, the ZF spectra exhibit an increasingly damped exponential form upon cooling, indicating emergence of local magnetism from freezing of electronic moments.,The nickelate samples reach a fully magnetic state across all doping levels at temperatures between 5 - 15 K.,The observation of broad peaks in the wTF depolarization rate reveal a wide distribution of spin relaxation timescales upon cooling.
  • The local-moment magnetic state is intrinsic and independent of superconductivity, with no anomaly at the superconducting transition in magnetic measurements.
    • Evidence: The persistence of a fully magnetic state across all samples indicates that magnetism is intrinsic, i.e., cannot be attributed to defects, and occurs independently of the hole concentration.,Notably, the behavior of the superconducting samples is qualitatively the same as the non-superconducting compositions.,We find that the emergence of intrinsic local magnetic moments occurs regardless of the doping level and we observe no anomalies in either ZF or wTF measurements at the superconducting transition temperature.
  • Increased hole doping weakly destabilizes the glassy magnetic state, as seen by lower peak temperatures and faster spin fluctuations.
    • Evidence: The peak in depolarization rate changes across the doping series, appearing to evolve from 40 K to 15 K as the doping is increased.,In contrast, the fluctuation rate increases with doping when measured at 40 K.,We also observe a subtle destabilization of the glassy state with increased hole doping.
  • Magnetism and superconductivity in infinite-layer nickelates are largely decoupled and their indirect interactions are best described in a multi-orbital framework.
    • Evidence: These observations suggest that magnetism and superconductivity are largely decoupled phenomena with indirect interactions described in a multi-orbital framework.,These findings point towards a multi-orbital electronic framework that allows magnetism and superconductivity to coexist.,The coexistence of magnetism and superconductivity suggests that local moments only weakly interact with the delocalized electrons that form Cooper pairs.

Workflow

  • sample_preparation — High-quality infinite-layer (La,Sr)NiO2 thin films were prepared across the full doping series.
    • Materials: (La,Sr)NiO2 thin-film doping series (Sr substitution 0% ≤ x ≤ 25%); (La,Sr)NiO3 perovskite precursor; CaH2 powder; SrTiO3 capping layer; Au overlayer
    • Methods: pulsed laser deposition (PLD) of perovskite precursor; topochemical reduction with CaH2 to infinite-layer phase; preparation of sample mosaics with ≥1 cm2 total surface area; X-ray diffraction and temperature-dependent resistivity characterization
    • Observations: XRD 2θ-ω scans confirm complete transition into infinite-layer phase; resistivity curves consistent with previously reported nickelate samples across phase diagram
  • measurement — Muon spin rotation/relaxation measured static and dynamic local magnetism across doping and temperature.
    • Materials: (La,Sr)NiO2 sample mosaics; low-energy muon beam at E4 beamline, Swiss Muon Source, Paul Scherrer Institut
    • Methods: low-energy muon spin rotation/relaxation (LEM/μSR); zero-field (ZF) geometry; weak transverse field (wTF) geometry; longitudinal field (LF) geometry with 25 and 100G; 3 keV incident muon energy with Monte Carlo depth-profile optimization
    • Observations: ZF asymmetry evolves from room-temperature paramagnetic behavior to increasingly damped exponential form on cooling; wTF magnetic volume fraction reaches a fully magnetic state at 5–15 K for all doping levels; wTF depolarization rate shows broad peaks near 40 K for underdoped and 15 K for overdoped samples; LF spectra show decaying asymmetry at 40 K and flattened asymmetry at 5 K under 100G
  • analysis — Spectral fitting quantified magnetic volume fraction, spin-freezing temperatures, and static/dynamic fluctuation parameters.
    • Materials: ZF, wTF, and LF μSR spectra
    • Methods: stretched exponential fits to ZF asymmetry; oscillatory wTF asymmetry fits to extract magnetic volume fraction and depolarization rate; frequency-dependent wTF peak shift analysis; dynamic Gaussian Kubo-Toyabe fits to LF spectra
    • Observations: β < 1 for all ZF curves, indicating electronic moments; wTF depolarization peak shifts from 40 K to 75 K with increasing Larmor frequency for x = 5%; extracted fluctuation rate at 40 K is at least 1.5× higher than at 5 K and increases with doping; Δ/ν ratio falls below 1 and decreases from 40 K to 5 K, showing growing static spin-freezing contribution
  • interpretation — Local-moment magnetism and glassy spin freezing are intrinsic, largely decoupled from superconductivity, and consistent with a multi-orbital framework.
    • Materials: μSR-derived magnetic parameters; doping-dependent phase diagram
    • Methods: comparison with cuprate and conventional spin glass behavior; evaluation of multi-orbital and RKKY interaction scenarios; discussion of possible high-spin/low-spin doped-hole configurations
    • Observations: fully magnetic intrinsic state persists across the superconducting dome; no anomaly at superconducting transition; glass onset near 40 K similar across doping; weak doping-dependent destabilization