Altermagnetic polar metallic phase in ultra-thin epitaxially-strained RuO₂ film

Altermagnetism, a newly discovered magnetic state, has garnered significant interest in both fundamental research and spintronics. Characterized by invariance under the combination of time reversal and crystal rotation, its manifestation in RuO₂ remains highly debated. In this talk, by employing scattering techniques, microscopy, spectroscopy, electrical transport measurements, and theoretical modeling, we elucidate the structure-property relationship in hybrid MBE-grown RuO₂ films. Metallic behavior is observed down to 0.8 nm, attributed to excellent defect control via hybrid MBE. We further investigate the correlation between crystal symmetry, electronic structure, and transport properties in epitaxial strained RuO₂, consistent with a novel polar, altermagnetic, metallic phase. These results pave the way for understanding and modulating novel altermagnetic phases via epitaxial heterostructure design.