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DOE OSTI2021

Magnetic Weyl Semimetallic Phase in Thin Films of Eu 2 Ir 2 O 7

The interplay between electronic interactions and strong spin-orbit coupling is expected to create a plethora of fascinating correlated topological states of quantum matter. Of particular interest are magnetic Weyl semimetals originally proposed in the pyrochlore iridates, which are only expected to reveal their topological nature in thin film form. To date, however, direct experimental demonstrations of these exotic phases remain elusive, due to the lack of usable single crystals and the insufficient quality of available films. Here, in this study, we report on the discovery of signatures for the long-sought magnetic Weyl semimetallic phase in (111)-oriented Eu 2 Ir 2 O 7 high-quality epitaxial thin films. We observed an intrinsic anomalous Hall effect with colossal coercivity but vanishing net magnetization, which emerges right below the onset of a peculiar magnetic phase with all-in-all-out (AIAO) antiferromagnetic ordering. The anomalous Hall conductivity obtained experimentally is consistent with the theoretical prediction, likely arising from the nonzero Berry curvature emanated by Weyl node pairs near the Fermi level that act as sources and sinks of Berry flux, activated by broken cubic crystal symmetry at the top and bottom terminations of the thin film.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering

We report new precision measurements of the elastic electron-proton scattering cross section for momentum transfer squared (Q$^2$) up to 15.75 (GeV/c)$^2$. These data allow for improved extraction of the proton magnetic form factor at high Q$^2$ and nearly double the Q$^2$ range of direct longitudinal/transverse separated cross sections. A comparison of our results to polarization measurements establishes the presence of hard two-photon exchange in the $e$-$p$ elastic scattering cross section at > 95 % confidence level for Q$^2$ up to 8 (GeV/c)$^2$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗