Zeeman spin-orbit coupling in antiferromagnetic conductors

Abstract

We find that the Néel state of the layered organic conductor κ-(BETS)2FeBr4 shows no spin modulation of the Shubnikov-de Haas oscillations, contrary to the paramagnetic state of the same material. This is evidence of spin degeneracy of Landau levels -a direct manifestation of the generic Zeeman spin-orbit coupling, predicted for antiferromagnetic conductors. Likewise, we find no spin modulation in the angle dependence of the slow Shubnikov-de Haas oscillations in the optimally electron-doped cuprate Nd2−xCexCuO4. This points to the presence of Néel order in this superconductor even at optimal doping.

Symmetry-enforced Dirac points in antiferromagnetic semiconductors

“…This is usually observed experimentally as the absence of g-factors in quantum oscillation measurements [16]. This is again related to the fact that the spin rotation together with the time reversal operation and the AFM translation is the true symmetry operation in the AFM crystal [14,15]. In this paper using AFM crystal GdB 4 as an example, I show that the symmetry enforced Dirac points exist at some high symmetry points of the BZ.…”

“…( 6)) is preserved on the line determined by the conditions k z = 0 and k x ± k y = 0. Second order invariants lift this degeneracy everywhere except M and A points of the BZ [14,15].…”

“…Usually application of the magnetic field in ordinary metals and semiconductors lifts the Kramers degeneracy. In AFM conductors there are special points in the BZ where the Kramers degeneracy is preserved when the magnetic field is perpendicular to the sublattice magnetization of the AFM conductor [14,15]. This is usually observed experimentally as the absence of g-factors in quantum oscillation measurements [16].…”