Seminarium Fizyki Materii Skondensowanej

The Kramers’ degeneracy was born in the field of spectroscopy for systems with time-reversal symmetry. Under the additional condition of the inversion symmetry was applied also to the field of the solid-state physics for non-magnetic systems. Recently, it was shown that the extension of the Kramers’degeneracy to the antiferromagnetic systems has some limitations. Without spin-orbit coupling, some antiferromagnets does not present Kramers’degeneracy but a large non-relativistic spin-splitting due to the breaking of time-reversal symmetry. This antiferromagnetism without Kramers degeneracy was named altermagnetism. Altermagnetic compounds behave as conventional antiferromagnets in the real space and as ferromagnets in the k-space paving the way for new technological applications.The presence of the altermagnetic phase strongly depends on the magnetic space group. We investigate the altermagnetic properties of strongly-correlated transition metal oxides analyzing the Mott insulators Ca2RuO4 and YVO3. In both cases, the orbital physics is extremely relevant in the t2g subsector with the presence of an orbital-selective Mott physics in the first case and of a robust orbital-order in the second case. I will briefly mention how the nonsymmorphic symmetries and the dimensionality affect the properties of the altermagnetic phase.Including the spin-orbit coupling, we study the effect of Dzyaloshinskii–Moriya interaction (DMI) in centrosymmetric and noncentrosymmetric altermagnets. Once time-reversal symmetry is broken in altermagnets, the DMI can produce weak ferromagnetism or weak ferrimagnetism from a purely relativistic effect. The DMI that generated weak ferromagnetism in altermagnets has a staggered structure and the DMI can be enhanced by adapting to the staggered geometry the same strategies used to increase DMI in ferromagnetic multilayers. The weak ferromagnetism from a purely relativistic effect is a property exclusively of the altermagnets that is not found in either ferromagnets or conventional antiferromagnets.