ABSTRACT: Spintronics, focused on transport of spins carried by itinerant electrons and their interaction with localized spins hosted by magnetic layers within multilayered heterostructures, has been one of the most active research subfields of condensed matter and materials physics. This is largely due to its unique synergy between abundant experimental data, fundamental theoretical challenges, search for new materials and technology transfer. Arguably, the two key phenomena of contemporary spintronic research are spin torque [1], where itinerant electrons exchange spin angular momentum with localized spins; and spin pumping [2], where dynamical localized spins generate spin current in the absence of any bias voltage. Their standard theoretical description is essentially quantum-classical, where flowing electrons and their spins are treated quantum-mechanically, while localized spins are treated as classical vectors obeying phenomenological Landau-Lifshitz-Gilbert equation that is widely believed to be justified by finite temperature and dissipation [3]. However, recent path-breaking experiments have witnessed entanglement in antiferromagnets and quantum spin liquids via inelastic neutron scattering up to surprisingly high temperature [4]. This talk will discuss the fate of entanglement [3] of many localized spins within antiferromagnetic or quantum spin liquid solids, as well as how its presence can dramatically modify spin torque [1,5] and pumping effects. This, in turn, can then be exploited to probe such exotic phases via the toolbox of spintronic phenomena and experimental techniques. In addition, it will also cover theory of table-top experiment which can extract dynamic spin structure factor and quantum Fisher information as the witness of entanglement in quantum magnets while not requiring large facilities and three-dimensional crystals as in inelastic neutron scattering.
REFERENCES:
[1] M. D. Petrović, P. Mondal, A. E. Feiguin, P. Plecháč, and B. K. Nikolić, Spintronics meets density matrix renormalization group: Quantum spin torque driven nonclassical magnetization reversal and dynamical buildup of long-range entanglement, Phys. Rev. X 11, 021062 (2021).
[2] J. Varela-Manjarres and B. K. Nikolić, High-harmonic generation in spin and charge current pumping at ferromagnetic or antiferromagnetic resonance in the presence of spin-orbit coupling, J. Phys. Mater. 6, 045001 (2023).
[3] F. Garcia-Gaitan and B. K. Nikolić, Fate of entanglement in ferro- and antiferromagnets under Lindbladian or non-Markovian dynamics and conditions for transition to classical Landau-Lifshitz dynamics, Phys. Rev. B 109, L180408 (2024).
[4] A. O. Scheie et al., Proximate spin liquid and fractionalization in the triangular antiferromagnet KYbSe2, Nat. Phys. 20, 74 (2024).
[5] M. D. Petrović, P. Mondal, A. E. Feiguin, and B. K. Nikolić, Quantum spin torque driven transmutation of antiferromagnetic Mott insulator, Phys. Rev. Lett. 126, 197202 (2021).