Strain, doping, and defects in MnTe and RuO₂

Altermagnets form a recently identified class of collinear magnets that exhibit momentum-dependent spin splitting despite having no net magnetization. In this talk, we use first-principles calculations to examine how strain, point defects, and doping modify the electronic structure and affect the interpretation of measurements probing altermagnetic order in two representative systems.

First, in RuO₂, experimental studies on bulk crystals and thin films have yielded conflicting evidence as to whether the material exhibits magnetic order. By comparing first-principles results with measurements of electronic, optical, and vibrational properties, we find that the nonmagnetic state provides the most consistent description of bulk RuO₂. Our calculations show that epitaxial strain has a distinct influence on magnetic order; RuO₂ strained to TiO₂ (110) develops weak magnetic ordering, whereas strain to TiO₂ (001) does not induce magnetism.  Second, in MnTe, a semiconductor that exhibits altermagnetic order, both bulk and thin-film samples exhibit unintentional p-type conductivity, though their resistivity shows distinct temperature dependences. Using first-principles calculations, we analyze possible sources of p-type behavior and discuss the influence of band offsets on transport measurements in MnTe thin films.