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Register a new userIsotropic Kink and Quasiparticle Excitations in the Three-Dimensional Perovskite Manganite La$_{0.6}$Sr$_{0.4}$MnO$_3$
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In order to reveal many-body interactions in the three-dimensional (3D) perovskite manganite, we have performed an $in$ $situ$ angle-resolved photoemission spectroscopy (ARPES) on La$_{0.6}$Sr$_{0.4}$MnO$_3$ (LSMO) and investigated the behaviors of quasiparticles. We observe quasiparticle peaks around the Fermi momentum, both in the electron and the hole bands, and clear kinks throughout the hole Fermi surface in the ARPES band dispersion. The isotropic behavior sharply contrasts to the strong anisotropic quasiparticle excitation observed in layered manganites. These results suggest that polaronic quasiparticles by coupling of the electrons with Jahn-Teller phonons play an important role in the physical properties of the ferromagnetic metallic phase in 3D manganite LSMO.
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We investigated slow relaxations of the magnetostriction and residual magnetostriction of the phase-separated system (Eu$_{1-x}$Gd$_{x}$)$_{0.6}$Sr$_{0.4}$MnO$_3$, in which the metamagnetic transition from a paramagnetic insulating state to a ferromagnetic metallic state is accompanied by a lattice shrinkage. The relaxations are well fitted by a stretched exponential function, suggesting the strong frustraction between the double exchange interaction and Jahn-Teller effect. We have revealed that the Gd substitution suppresses the frozen phase-separated phase at low temperatures and stabilizes the paramagnetic insulating state in the dynamic phase-separated phase at intermediate temperatures. The former origin would be the randomness effect and the latter would be the suppression of the double exchange interaction.
Effect of hydrostatic pressure and magnetic field on electrical resistance of the Kondo-like perovskite manganese oxide, La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$ with a ferrimagnetic ground state, have been investigated up to 2.1 GPa and 9 T. In this compound, the Mn-moments undergo double exchange mediated ferromagnetic ordering at $T_{rm C}$ $sim$ 280 K and there is a resistance maximum, $T_{rm max}$ at about 130 K which is correlated with an antiferromagnetic ordering of {it cerium} with respect to the Mn-sublattice moments. Under pressure, the $T_{rm max}$ shifts to lower temperature at a rate of d$T_{max}$/d$P$ = -162 K/GPa and disappears at a critical pressure $P_{rm c}$ $sim$ 0.9 GPa. Further, the coefficient, $m$ of $-logT$ term due to Kondo scattering decreases linearly with increase of pressure showing an inflection point in the vicinity of $P_{rm c}$. These results suggest that {it cerium} undergoes a transition from Ce$^{3+}$ state to Ce$^{4+}$/Ce$^{3+}$ mixed valence state under pressure. In contrast to pressure effect, the applied magnetic field shifts $T_{rm max}$ to higher temperature presumably due to enhanced ferromagnetic Mn moments.
Using polarized neutron reflectometry (PNR), we observe an induced magnetization of 75$pm$ 25 kA/m at 10 K in a La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO)/BiFeO$_3$ superlattice extending from the interface through several atomic layers of the BiFeO$_3$ (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of bandgap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.
We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr$_{0.5}$Ca$_{0.5}$MnO$_3$ and ferromagnetic metallic La$_{0.5}$Sr$_{0.5}$MnO$_3$ by resonant soft x-ray diffraction. A temperature-dependent incommensurability is found in the orbital order. In addition, a large hysteresis is observed that is caused by phase competition between insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to bulk, confirming the unique character of the superlattice. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to a decoupling of the orbital-ordered planes along the c axis.
We investigate the high temperature phase of layered manganites, and demonstrate that the charge-orbital phase transition without magnetic order in La$_{0.5}$Sr$_{1.5}$MnO$_4$ can be understood in terms of the density wave instability. The orbital ordering is found to be induced by the nesting between segments of Fermi surface with different orbital characters. The simultaneous charge and orbital orderings are elaborated with a mean field theory. The ordered orbitals are shown to be $d_{x^2-y^2} pm d_{3z^2-r^2}$.
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