Altermagnetism presents intriguing possibilities for spintronic devices due to its unique combination of strong spin-splitting and zero net magnetization. However, realizing its full potential hinges on fabricating single-variant altermagnetic thin films. In this work, we present definitive evidence for formation of single-variant altermagnetic RuO2(101) thin films with fully epitaxial growth on Al2O3(1 \(\bar{1}\) 02) r-plane substrates, confirmed through rigorous structural analyses using X-ray diffraction, atomic-resolution transmission electron microscopy and X-ray magnetic linear dichroism. The mutual correspondence of the occupancy of oxygen atoms on the surfaces of RuO2(101)[010] and Al2O3(1 \(\bar{1}\) 02)[11 \(\bar{2}\) 0] plays a decisive role in the formation of the single-variant RuO2, which is also supported by our first-principles density functional theory calculations. We further observed spin-splitting magnetoresistance in the single-variant RuO2(101)/CoFeB bilayers, highlighting the characteristic effect of single variant on spin transport. The demonstration of single-variant RuO2(101) films marks a significant advancement in the field of altermagnetism and paves the way for exploring their potential applications.
