Ahmed I. Lobad

Spin–lattice interaction in colossal magnetoresistance manganites

The metal–insulator transition and underlying spin dynamics in La0.7D0.3MnO3 (D=Ca, Sr) are investigated using optical pump–probe spectroscopy at 1.5 eV. Our measurements, which span the ferromagnetic–paramagnetic transition temperature, reveal that the dynamics of the optically induced spectral weight transfer follow the temperature dependence of the magnetic specific heat. This dependence reflects the intrinsic interdependence between the optical conductivity and magnetism in the manganites allowing for the determination of the spin-lattice coupling magnitude.

Laser induced dynamic spectral weight transfer in La0.7Ca0.3MnO3

Abstract We report on optical pump-probe measurements at 1.5 eV and 3 eV on the colossal magnetoresistance material La 0.7 Ca 0.3 MnO 3 . The material response is determined in the femtosecond to the nanosecond temporal regimes. By analyzing the absorption and refractive dynamics within the Kramers–Kronig transformations we demonstrate dynamic spectral weight transfer from the intraband Drude component to the interband transitions. This spectral transfer and its strongly temperature dependent dynamics are discussed in the framework of photoinduced demagnetization due to the exchange of energy and thermal equilibration among the electronic, lattice and spin systems. This effect is observed in other manganites with different transition temperatures. The measured dynamics are found to be insensitive to the excitation photon energy.

Femtosecond studies of mixed valence state formation in strongly correlated electron materials

Abstract We present the results of our ultrafast optical experiments on mixed-valence manganites La 0.7 X 0.3 MnO 3 ( X = Ca, Sr ) and the heavy-fermion compounds YbXCu 4 ( X = Ag, In ) . For the manganites, 1.5 eV pump and either optical or terahertz probe reveals a dynamic spectral weight transfer that, as a function of temperature, allows us to determine the spin–lattice relaxation time. For YbXCu4, pump–probe measurements at 1.5 eV are shown to be sensitive to the onset of coherence. These results are discussed in terms of a simple hybridization gap model for the f and s electrons.

Ultrafast THz conductivity dynamics: spinlattice relaxation in colossal magnetoresistive oxides

Ultrafast measurements of optically induced changes in the conductivity (0.4-1.0 THz) of La0.7M0.3MnO3 films (M = Ca, Sr) from -10K to -0.9Tc reveal a spin-lattice relaxation that follows the temperature dependence oftbe spin specific heat.