Observation of the anomalous Nernst effect in altermagnetic candidate Mn₅Si₃

The anomalous Nernst effect generates a voltage transverse to an applied thermal gradient in some magnetically ordered systems. While the effect was considered excluded in compensated magnetic materials with collinear ordering, in the recently identified symmetry-class of altermagnets, the anomalous Nernst effect is possible despite the compensated collinear spin arrangement. In this work, we show that epitaxial Mn₅Si₃ thin films grown on Si manifest an anomalous Nernst effect with a finite spontaneous signal at zero magnetic field despite the vanishing spontaneous magnetization. We attribute this to the previously theoretically predicted and experimentally corroborated altermagnetism of epitaxial Mn₅Si₃ thin films grown on Si. The observed spontaneous anomalous Nernst coefficient reaches the value of 0.26 μV/K with the corresponding spontaneous Nernst conductivity of 0.22 A/(K  ⋅  m). To complement our measurements, we perform density-functional theory calculations of the momentum-resolved anomalous Nernst conductivity, highlighting the contributions of altermagnetic pseudonodal surfaces and ladder transitions to the Berry curvature. Our results illustrate the value of unconventional d-wave wave altermagnets composed of abundant and non-toxic light elements for thermo-electrics and spin-caloritronics.