Month: January 2024

A joint publication with Jairo Sinova, Libor Šmejkal and Anna Hellenes about the observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO2 has been published in Science Advances.

They directly observe strong time-reversal symmetry breaking in the band structure of altermagnetic RuO2 by detecting magnetic circular dichroism in angle-resolved photoemission spectra. Their experimental results, supported by ab initio calculations, establish the microscopic electronic structure basis for a family of interesting phenomena and functionalities in fields ranging from topological matter to spintronics, which are based on the unconventional time-reversal symmetry breaking in altermagnets.

A joint publication with Jairo Sinova and Libor Šmejkal about the crystal thermal transport in altermagnetic
RuO2 has been published in Physical Review Lettters.

They demonstrate the emergence of a pronounced thermal transport in the recently discovered class of magnetic materials—altermagnets. From symmetry arguments and first-principles calculations performed for the showcase altermagnet, RuO2, they uncover that crystal Nernst and crystal thermal Hall effects in this material are very large and strongly anisotropic with respect to the Néel vector. They find the large crystal thermal transport to originate from three sources of Berry’s curvature in momentum space: the Weyl fermions due to crossings between well-separated bands, the strong spin-flip pseudonodal surfaces, and the weak spin-flip ladder transitions, defined by transitions among very weakly spin-split states of similar dispersion crossing the Fermi surface. Moreover, they reveal that the anomalous thermal and electrical transport coefficients in RuO2 are linked by an extended Wiedemann-Franz law in a temperature range much wider than expected for conventional magnets. Their results suggest that altermagnets may assume a leading role in realizing concepts in spin caloritronics not achievable with ferromagnets or antiferromagnets.

A joint publication with Jairo Sinova, Libor Šmejkal and Helen Gomonay about phase transitions associated with magnetic-field induced topological orbital momenta in a non-collinear antiferromagnet has been published in Nature communications.

They show that in polycrystalline Mn3Zn0.5Ge0.5N with non-collinear antiferromagnetic order, changes in the diagonal and, rather unexpected, off-diagonal components of the resistivity tensor occur at low temperatures indicating subtle transitions between magnetic phases of different symmetry. This is supported by neutron scattering and explained within a phenomenological model which suggests that the phase transitions in magnetic field are associated with field induced topological orbital momenta. The fact that they observe transitions between spin phases in a polycrystal, where effects of crystalline anisotropy are cancelled suggests that they are only controlled by exchange interactions. The observation of an off-diagonal resistivity extends the possibilities for realising antiferromagnetic spintronics with polycrystalline materials.

A joint publication with Libor Šmejkal about the broken Kramers degeneracy in altermagnetic MnTe has been published in Physical Review Letters.

By combining high-quality film growth and in situ angle-resolved photoemission spectroscopy, they report the electronic structure of an altermagnetic candidate, $\alpha \text{−}\mathrm{MnTe}$. Temperature-dependent study reveals the lifting of Kramers degeneracy accompanied by a magnetic phase transition at $T_N=267K$with spin splitting of up to 370 meV, providing direct spectroscopic evidence for altermagnetism in MnTe.