Ultrafast reorientation of the Néel vector in antiferromagnetic Dirac semimetals*

It is recognized that in a class of antiferromagnets with parity-time symmetry the Néel vector can be switched by staggered (Néel) spin-orbit torque (NSOT) generated by the electric currents, and furthermore an additional nonsymmorphic crystalline symmetry enables the control of the Dirac quasiparticles via the direction of the Néel vector. However, the real-time dynamics of the magnetic and the microscopic electronic structures induced by the NSOT is still largely unknown from theoretical and experimental viewpoints. We propose a theoretical framework for the ultrafast dynamics in AFM Dirac semimetals, taking not only localized magnetic moments but also itinerant electrons into account. We show that the Néel vector is rotated in picosecond timescales by the current- and the terahertz-pulse-induced NSOT as well as a magnetic anisotropy, which accompanies the modulation of the mass of the Dirac quasiparticles. It is also found that this reorientation can be experimentally observed through the time-resolved quadratic magneto-optical Kerr effect.