39 research outputs found
Collective magnetization dynamics in ferromagnetic (Ga,Mn)As mediated by photo-excited carriers
We present a study of photo-excited magnetization dynamics in ferromagnetic
(Ga,Mn)As films observed by time-resolved magneto-optical measurements. The
magnetization precession triggered by linearly polarized optical pulses in the
absence of an external field shows a strong dependence on photon frequency when
the photo-excitation energy approaches the band-edge of (Ga,Mn)As. This can be
understood in terms of magnetic anisotropy modulation by both laser heating of
the sample and by hole-induced non-thermal paths. Our findings provide a means
for identifying the transition of laser-triggered magnetization dynamics from
thermal to non-thermal mechanisms, a result that is of importance for ultrafast
optical spin manipulation in ferromagnetic materials via non-thermal paths.Comment: 11 pages, 9 figure
Light control of surface–bulk coupling by terahertz vibrational coherence in a topological insulator
The demand for disorder-tolerant quantum logic and spin electronics can be met by generating and controlling dissipationless spin currents protected by topology. Dirac fermions with helical spin-locking surface transport offer a way of achieving such a goal. Yet, surface-bulk coupling can lead to strong Dirac electron scattering with bulk carriers and phonons as well as impurities, assisted by such dissipative channel, which results in “topological breakdown”. Here, we demonstrate that coherent lattice vibrations periodically driven by a single-cycle terahertz (THz) pulse can significantly suppress such dissipative channel in topological insulators. This is achieved by reducing the phase space in the bulk available for Dirac fermion scattering into during coherent lattice oscillations in Bi2Se3. This light-induced suppression manifests as a remarkable transition exclusively in surface transport, absent for bulk, above the THz electric fields for driving coherent phonons, which prolongs the surface transport lifetime. These results, together with simulations, identify the critical role of spin–orbit coupling for the “phase space contraction” mechanism that suppresses the surface-bulk coupling. Imposing vibrational quantum coherence into topological states of matter may become a universal light control principle for reinforcing the symmetry-protected helical transport
All Optical Implementation of Multi-Spin Entanglement in a Semiconductor Quantum Well
We use ultrafast optical pulses and coherent techniques to create spin
entangled states of non-interacting electrons bound to donors (at least three)
and at least two Mn2+ ions in a CdTe quantum well. Our method, relying on the
exchange interaction between localized excitons and paramagnetic impurities,
can in principle be applied to entangle a large number of spins.Comment: 17 pages, 3 figure