1,291 research outputs found
Thermalization of magnons in yttrium-iron garnet: nonequilibrium functional renormalization group approach
Using a nonequilibrium functional renormalization group (FRG) approach we
calculate the time evolution of the momentum distribution of a magnon gas in
contact with a thermal phonon bath. As a cutoff for the FRG procedure we use a
hybridization parameter {\Lambda} giving rise to an artificial damping of the
phonons. Within our truncation of the FRG flow equations the time evolution of
the magnon distribution is obtained from a rate equation involving
cutoff-dependent nonequilibrium self-energies, which in turn satisfy FRG flow
equations depending on cutoff-dependent transition rates. Our approach goes
beyond the Born collision approximation and takes the feedback of the magnons
on the phonons into account. We use our method to calculate the thermalization
of a quasi two-dimensional magnon gas in the magnetic insulator yttrium-iron
garnet after a highly excited initial state has been generated by an external
microwave field. We obtain good agreement with recent experiments.Comment: 16 pages, 6 figures, final versio
Phonon-induced disorder in dynamics of optically pumped metals from non-linear electron-phonon coupling
The non-equilibrium dynamics of matter excited by light may produce
electronic phases that do not exist in equilibrium, such as laser-induced
high- superconductivity. Here we simulate the dynamics of a metal driven
at by a pump that excites dipole-active vibrational modes that couple
quadratically to electrons, and study the evolution of its electronic and
vibrational observables. We provide evidence for enhancement of local
electronic correlations, including double occupancy, accompanied by rapid loss
of long-range spatial phase coherence. Concurrently, the onsite vibrational
reduced density matrix evolves from its initial coherent state to one with a
predominantly diagonal structure whose distribution qualitatively resembles the
coherent state Poisson character. This rapid loss of coherence controls the
electronic dynamics as the system evolves towards a correlated electron-phonon
long-time state. We show that a simple model based on an effective disorder
potential generated by the oscillator dephasing dynamics for the electrons
provides an explanation for the flattening in momentum of electronic
correlations. Our results provide a basis within which to understand
correlation dynamics of vibrationally coupled electrons in pump-probe
experiments.Comment: 7 pages main text + 3 pages appendices, 5 figures main text + 2
figures appendice
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