Spectrally sharp magnetic excitations above the critical temperature in Weyl semimetals of rare-earth iridates

The rare-earth pyrochlore iridates represent a fascinating class of materials where electronic correlations, strong spin-orbit coupling, and geometrical frustration converge to create a variety of complex magnetic and electronic phases. Despite their intriguing properties, the magnetic order and excitations in these topological quantum materials are not well understood, primarily due to the difficulty in growing sizable high-quality single crystals and the lack of detailed microscopic insights into their temperature-dependent phases. In this talk, I will present the investigation into the magnetic excitations of Y₂Ir₂O₇ across the non-collinear antiferromagnetic transition using a combination of resonant elastic and inelastic X-ray scattering, spin-wave analysis and dynamical spin susceptibility calculations. Our results reveal the presence of unusual spectrally sharp, gapped magnetic excitations, which surprisingly persist far above the Néel transition temperature into the spin frustrated state. These findings reveal the existence of an unconventional cooperative paramagnetic (CP) phase governed by a hidden degree of freedom coupled with magnetic fluctuations. These results also provide new insight into the long-standing puzzling magnetic behavior in high temperatures across the family of semi-metallic pyrochlore iridates.