Fragile unconventional magnetism in RuO2 by proximity to Landau-Pomeranchuk instability

Altermagnetism has attracted considerable attention for its remarkable combination of spin-polarized band structures and zero net magnetization, making it a promising candidate for spintronics applications. We demonstrate that this magnetic phase represents a case of unconventional magnetism, first proposed nearly two decades ago as part of a broader framework for understanding Landau-Pomeranchuk instabilities in the spin channel, driven by many-body interactions. By systematically analyzing the altermagnetism in RuO2 with first-principles calculations, we reconcile conflicting experimental and theoretical reports by attributing it to RuO2's proximity to a quantum phase transition. We emphasize the critical role of tuning parameters, such as the Hubbard U , hole doping, and epitaxial strain, in modulating quasiparticle interactions near the Fermi surface. This work provides fresh insights into the origin and tunability of altermagnetism in RuO2, highlighting its potential as a platform for investigating quantum phase transitions and the broader realm of unconventional magnetism.