Metallic antiferromagnets are essential for efficient spintronic applications due to their fast switching and high mobility, yet room-temperature metallic antiferromagnets are rare. Here, we investigate ${\mathrm{YbMn}}_2{\mathrm{Ge}}_2$, a room-temperature antiferromagnet, and establish it as an exfoliable layered metal with altermagnetic surface states. Using multiorbital Hubbard model calculations, we reveal that its robust metallic antiferromagnetic ordering is stabilized by electronic correlations and a partially nested Fermi surface. Furthermore, we show that ${\mathrm{YbMn}}_2{\mathrm{Ge}}_2$ hosts symmetry-protected topological Dirac crossings, connecting unique even-order spin-polarized surface states with parabolic and inverted Mexican-hat-like dispersion. Our findings position ${\mathrm{YbMn}}_2{\mathrm{Ge}}_2$ as a promising platform for exploring the interplay of correlation, topology, and surface altermagnetism of layered antiferromagnets.

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• Electronic structure
• Magnetic order
• Magnetism
• Topological materials
• Antiferromagnets
• Crystalline systems
• Approximation methods for many-body systems
• Density functional theory
• Hubbard model