Altermagnetic polar metallic phase in ultrathin epitaxially strained RuO 2 films - Seung Gyo Jeong; In Hyeok Choi; Sreejith Nair; Luca Buiarelli; Bita Pourbahari; Jin Young Oh; Bonnie Y.X. Lin; James M. LeBeau; Nabil Bassim; Daigorou Hirai; Ambrose Seo; Woo Seok Choi; et al. (Proceedings of the National Academy of Sciences, 2026)