Quantum spin torque driven transmutation of antiferromagnetic Mott insulator*

The standard model of spin-transfer torque in antiferromagnetic spintronics considers the exchange of angular momentum between quantum spins of flowing electrons and noncollinear-to-them localized spins treated as classical vectors. These vectors are assumed to realize Néel order in equilibrium, ↑↓…↑↓, and their dynamics is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many experimentally employed materials (such as NiO) are strongly correlated antiferromagnetic Mott insulators (AFMI) where the ground state is quite different from the unentangled Néel state. The ground state is entangled by quantum spin fluctuations, leading to zero expectation value of all localized spins so the LLG dynamics cannot even be initiated. Instead, a fully quantum treatment of both electrons and localized spins is necessary to capture the spin transfer. Here, we use the time-dependent density matrix renormalization group approach to predict how the injection of spin current into a normal metal coupled to AFMI induces a nonzero expectation value of AFMI localized spins.

[1] M. D. Petrovic, P. Mondal, A. E. Feiguin, and B. K. Nikolic, ArXiv:2009.11833v2 (2020).