The Fate of Entanglement in Magnetism and Its Witnessing via Spintronic-Based Schemes

The entanglement of many localized spins within solid magnetic materials is a topic of great basic and applied interest, particularly after becoming amenable to experimental scrutiny where recent neutron scattering experiments have witnessed macroscopic entanglement in the ground state of antiferromagnets persisting even at elevated temperatures. Furthermore, exotic magnetic materials, such as quantum spin liquid, are governed by long-range entanglement where the lack of experimental probes for its direct detection has also hampered confirming that candidate quantum materials really host such phase. On the other hand, it is common in spintronics and magnonics to assume that finite temperature and dissipative environment automatically ensure transition from quantum many-body entangled states of spins to their classical dynamics governed by the celebrated Landau-Lifshitz-Gilbert equation. We have very recently delineated [1] rigorous criteria for such transition to occur by analyzing dynamics of open quantum systems of many spins coupled to a dissipative environment. They also furnish examples of how specific classes of nonequilibrium magnets can generate stronger entanglement than in equilibrium. By integrating quantum spin liquids into spintronic devices, the presence of entanglement could be detected by its effect on spin-dependent transport measurements.<br/><br/>[1] F. Garcia-Gaitan and B. K. Nikolić, Phys. Rev. B <b>109</b>, L180408 (2024).