Nonclassical magnetization reversal by quantum spin torque of many-electron pulse: A time-dependent density matrix renormalization group study*

Using the time-dependent density matrix renormalization group (tDMRG) method, we study nonclassical effects in the spin-transfer torque (STT) exerted by the spin-polarized electron current on a one-dimensional quantum Heisenberg ferromagnetic chain. Unlike standard STT induced dynamics of magnetization viewed as a classical vector of fixed length, quantum STT allows for the establishment of quantum entanglement between spins. Magnetization reversal driven by quantum STT is nonclassical in the sense that no rotation from its initial state occurs. We extend the findings of Ref. [1], which dealt with single electron wave packets impinging onto many quantum spins. In contrast, the tDMRG method allows us to tackle a problem of many quantum electrons coupled to many quantum spins. The quantum local spins, initially oriented along the negative z-axis, undergo a reversal into the positive z-axis direction after interaction with the spin-up polarized current.

[1] P. Mondal, U. Bajpal, M. D. Petrović, P. Plechač, and B. K. Nikolić, Phys. Rev. B 99, 094431 (2019).