6 research outputs found
Ultrafast Enhancement of Ferromagnetism via Photoexcited Holes in GaMnAs
We report on the observation of ultrafast photo-enhanced ferromagnetism in
GaMnAs. It is manifested as a transient magnetization increase on a 100-ps time
scale, after an initial sub-ps demagnetization. The dynamic magnetization
enhancement exhibits a maximum below the Curie temperature Tc and dominates the
demagnetization component when approaching Tc. We attribute the observed
ultrafast collective ordering to the p-d exchange interaction between
photoexcited holes and Mn spins, leading to a correlation-induced peak around
20K and a transient increase in Tc.Comment: 4 page
Observation of inter-Landau-level quantum coherence in semiconductor quantum wells
Using three-pulse four-wave-mixing femtosecond spectroscopy, we excite a
non-radiative coherence between the discrete Landau levels of an undoped
quantum well and study its dynamics. We observe quantum beats that reflect the
time evolution of the coherence between the two lowest Landau level
magnetoexcitons. We interpret our observations using a many-body theory and
find that the inter Landau level coherence decays with a new time constant,
substantially longer than the corresponding interband magnetoexciton dephasing
times. Our results indicate a new intraband excitation dynamics that cannot be
described in terms of uncorrelated interband excitations.Comment: 5 pages, 5 figures, to appear in Phys. Rev. B Rapid Communication
Memory Effect in the Photoinduced Femtosecond Rotation of Magnetization in the Ferromagnetic Semiconductor GaMnAs
We report a femtosecond response in photoinduced magnetization rotation in the ferromagnetic semiconductor GaMnAs, which allows for detection of a four-state magnetic memory at the femtosecond time scale. The temporal profile of this cooperative magnetization rotation exhibits a discontinuity that reveals two distinct temporal regimes, marked by the transition from a highly non-equilibrium, carrier-mediated regime within the first 200 fs, to a thermal, lattice-heating picosecond regime