Skip to main content
Nubint
QUICK REVIEW

[Paper Review] Neutron Scattering Studies on the High-$T_c$ Superconductor La$_3$Ni$_2$O$_{7-δ}$ at Ambient Pressure

Tao Xie, Mengwu Huo|arXiv (Cornell University)|Jan 23, 2024
Magnetic and transport properties of perovskites and related materials5 citations
TL;DR

Elastic and inelastic neutron scattering on polycrystalline La3Ni2O7-δ at ambient pressure finds no long-range magnetic order down to 10 K and reveals a non-dispersive spin excitation near 45 meV, consistent with a strong interlayer coupling in a double-stripe AFM-like scenario.

ABSTRACT

After several decades of studies of high-temperature superconductivity, there is no compelling theory for the mechanism yet; however, the spin fluctuations have been widely believed to play a crucial role in forming the superconducting Cooper pairs. The recent discovery of high-temperature superconductivity near 80 K in the bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure provides a new platform to elucidate the origins of high-temperature superconductivity. We perform elastic and inelastic neutron scattering studies on a polycrystalline sample of La$_3$Ni$_2$O$_{7-δ}$ at ambient pressure. No magnetic order can be identified down to 10 K. The absence of long-range magnetic order in neutron diffraction measurements may be ascribed to the smallness of the magnetic moment. However, we observe a weak flat spin-fluctuation signal at $\sim$ 45 meV in the inelastic scattering spectra. The observed spin excitations could be interpreted as a result of strong interlayer and weak intralayer magnetic couplings for stripe-type antiferromagnetic orders. Our results provide crucial information on the spin dynamics and are thus important for understanding the superconductivity in La$_3$Ni$_2$O$_7$.

Motivation & Objective

  • Investigate whether La3Ni2O7-δ hosts magnetic order at ambient pressure and low temperature.
  • Characterize spin fluctuations and their energy/momentum dependence using elastic and inelastic neutron scattering.
  • Estimate the magnetic exchange interactions and assess possible magnetic ground states.
  • Compare observed spin dynamics with theoretical models and DFT phonon calculations to understand coupling mechanisms.
  • Relate findings to the broader context of high-Tc superconductivity in nickelates and their relation to cuprates/iron pnictides.

Proposed method

  • Neutron powder diffraction to search for long-range magnetic order at 10 K and 160 K.
  • Inelastic neutron scattering with multiple incident energies (Ei) to map spin and phonon excitations.
  • SpinW-based modeling of spin excitation spectra to extract exchange couplings.
  • Density functional theory (DFT) phonon calculations to compute dispersion and DOS for comparison with INS.
  • Data subtraction of high vs. low temperature INS spectra to isolate magnetic contributions.
Figure 1: Structure, electronic occupancy, and bulk electrical transport, magnetic and structural characterization of the La 3 Ni 2 O 7-δ polycrystalline sample. (a) Crystal structure of La 3 Ni 2 O 7-δ in the $Amam$ space group. The open blue circle represents an oxygen vacancy. (b) Schematic of th
Figure 1: Structure, electronic occupancy, and bulk electrical transport, magnetic and structural characterization of the La 3 Ni 2 O 7-δ polycrystalline sample. (a) Crystal structure of La 3 Ni 2 O 7-δ in the $Amam$ space group. The open blue circle represents an oxygen vacancy. (b) Schematic of th

Experimental results

Research questions

  • RQ1Is there long-range magnetic order in La3Ni2O7-δ at ambient pressure down to 10 K?
  • RQ2What is the nature of spin fluctuations and their energy scale in La3Ni2O7-δ at ambient pressure?
  • RQ3What are the magnitudes and hierarchy of magnetic exchange couplings (intralayer vs interlayer)?
  • RQ4Can a magnetic structure such as alternate double stripe AFM explain the observed spin excitations?],
  • RQ5key_findings([

Key findings

  • No magnetic Bragg peaks detected; no long-range magnetic order down to 10 K.
  • A weak flat spin-fluctuation signal centered near 45 meV in inelastic scattering spectra.
  • Spin excitation spectrum well described by an alternate double stripe AFM order with strong interlayer and weak intralayer couplings (SJ⊥ ≈ 36 meV; SJ1 ≈ 5; SJ2 ≈ -2; SJ4 ≈ 1).
  • Dispersive and non-dispersive phonon modes observed; DFT phonon dispersion and DOS roughly match INS features.
  • Strong interlayer magnetic exchange dominates spin dynamics, differing from cuprates and iron-based superconductors.
Figure 2: INS spectra of La 3 Ni 2 O 7-δ with different incident energies at low temperature. (a) INS spectrum collected at PELICAN with $E_{i}$ = 3.7 meV. (b) and (c) are INS spectra measured at MERLIN with $E_{i}$ = 22.6 and 160 meV, respectively. (d) INS spectrum up to 350 meV obtained at MAPS. (
Figure 2: INS spectra of La 3 Ni 2 O 7-δ with different incident energies at low temperature. (a) INS spectrum collected at PELICAN with $E_{i}$ = 3.7 meV. (b) and (c) are INS spectra measured at MERLIN with $E_{i}$ = 22.6 and 160 meV, respectively. (d) INS spectrum up to 350 meV obtained at MAPS. (

Better researchstarts right now

From reading papers to final review, dramatically reduce your research time.

No credit card · Free plan available

This review was created by AI and reviewed by human editors.