Altermagnets, a distinctive class of unconventional antiferromagnets featuring compensated magnetization but ferromagnetlike spin splitting, have attracted significant interest as promising candidates for next-generation memories. Here, we design an altermagnetic tunnel junction (AMTJ) based on the room-temperature altermagnetic metal ${\mathrm{RbV}}_2{\mathrm{Te}}_2\mathrm{O}$ and systematically explore its interfacial and transport properties via first-principles calculations. We found that the strong interfacial V-O bonding effectively bridges the separated magnetic V atomic chains across the barrier, resulting in an ultralow resistance-area (RA) product of $\sim 3.82\mathrm{\Omega }\mu {\mathrm{m}}^2$. In contrast, the substitution of other types of interfacial bonds disrupts the V chain connectivity and dramatically increases device RA up to $\sim 2.55\times {10}^7\mathrm{\Omega }\mu {\mathrm{m}}^2$. Moreover, the ${\mathrm{RbV}}_2{\mathrm{Te}}_2\mathrm{O}/{\mathrm{SrTiO}}_3/{\mathrm{RbV}}_2{\mathrm{Te}}_2\mathrm{O}$ AMTJ exhibits a giant tunneling magnetoresistance (TMR) of $\sim 6.58\times {10}^{12}\%$, owing to the high effective spin polarization of ${\mathrm{RbV}}_2{\mathrm{Te}}_2\mathrm{O}$ and excellent momentum overlap with lowest-decay-rate evanescent states in the ${\mathrm{SrTiO}}_3$ barrier. Our work proposes an alternative strategy—engineering strong interfacial bonding along the magnetic atomic chains—aside from conventional approaches such as high spin polarization and momentum matching, to simultaneously minimize RA while maximizing TMR within a single AMTJ. These findings inspire further exploration of AM-based spintronics.

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• Electronic structure
• Spintronics
• Altermagnets
• Interfaces
• Tunnel junctions
• First-principles calculations