Interlayer dispersion of spin waves in La₂CuO₄ investigated by neutrons using diffraction method

The high-temperature superconductivity in cupric oxides remains enigmatic despite being intensely researched for over nearly four decades. These materials are derived from parent antiferromagnetic Mott insulator oxides, such as La₂CuO₄ (LCO). Neutron scattering measurements of magnetic structures and excitations provided significant insight into electronic properties of these materials. The low-energy electronic dynamics, superconductivity, and stripe-ordered phases are all intertwined with magnetism. While the in-plane magnetic interactions have been thoroughly characterized through spin-wave dispersion measurements with neutrons, the inter-layer magnetic interaction which renders the inter-plane spin wave dispersion has not been well-characterized. This is because the spin-wave signal in cuprates is weak and full measurement of magnetic excitation spectrum on a neutron spectrometer is very time-consuming. Hence, the interlayer dispersion is usually integrated over to improve the signal. Understanding the strength of magnetic inter-layer interaction in LCO and its evolution with doping in the derived superconductor family is important because this coupling is sensitive to the inter-layer arrangement of charge stripes in the doped compositions and position and dynamics of the apical oxygens, which are important for superconductivity. It might also be relevant for an unusually large thermal Hall conductivity which was tentatively ascribed to chiral phonons. Here, we report measurements of the inter-plane dispersion of spin waves in LCO using diffraction method, which we recently reinvented. This method uses a neutron diffractometer with large, highly pixelated area-sensitive detector without energy analysis and provides significant rise in throughput.