Abstract
We study the unitary time evolution of antiferromagnetic order in the Hubbard model after a quench starting from the perfect N\'eel state. In this setup, which is well suited for experiments with cold atoms, one can distinguish fundamentally different pathways for melting of long-range order at weak and strong interaction. In the Mott insulating regime, melting of long-range order occurs due to the ultra-fast transfer of energy from charge excitations to the spin background, while local magnetic moments and their exchange coupling persist during the process. The latter can be demonstrated by a local spin-precession experiment. At weak interaction, local moments decay along with the long-range order. The dynamics is governed by residual quasiparticles, which are reflected in oscillations of the off-diagonal components of the momentum distribution. Such oscillations provide an alternative route to study the prethermalization phenomenon and its influence on the dynamics away from the integrable (noninteracting) limit. The Hubbard model is solved within nonequilibrium dynamical mean-field theory, using the density matrix-renormalization group as an impurity solver.
Highlights
Ultrafast pump-probe experiments on condensed-matter systems and experiments with cold gases in optical lattices have opened the intriguing possibility of controlling transitions between complex phases on microscopic time scales
We find qualitatively different relaxation behaviors for weak and strong interactions, separated by a crossover around U ≈ 0.6 × bandwidth: For strong interaction, local magnetic moments persist while their order is destroyed by spin flips due to the hopping of mobile charges
To demonstrate the persistence of local moments, we propose a spin-precession experiment, which could be implemented similar to the proposed measurement of dynamic spin-spin correlation functions in equilibrium [59]
Summary
Ultrafast pump-probe experiments on condensed-matter systems and experiments with cold gases in optical lattices have opened the intriguing possibility of controlling transitions between complex phases on microscopic time scales. Magnetic order could possibly melt via the destruction of the local moments themselves, through a reduction of the effective exchange interaction [23] (while moments persist), or along a quasithermal pathway, by the transfer of energy from excited quasiparticles (hot electrons) to spins The latter mechanism is intensively studied in the context of.
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