Orbital reconstruction at the LAO/STO interface investigated by x-ray spectroscopy

Orbital reconstruction at the LAO/STO interface investigated by x-ray spectroscop

Angle Resolved Photoemission from Nd1.85Ce0.15CuO4 using High Energy Photons: A Fermi Surface Investigation

We have performed an angle resolved photoemission study on a single crystal of the optimally electron doped (n-type) cuprate superconductor Nd2xCexCuO4 (x 0:15) at a photon energy of 400 eV. The Fermi surface is mapped out and is, in agreement with earlier measurements, of hole-type with the expected Luttinger volume. However, comparing with previous low energy measurements, we observe a different Fermi surface shape and a different distribution of spectral intensity around the Fermi surface contour. The observed Fermi surface shape indicates a stronger electron correlation in the bulk as compared to the surface

Resonant inelastic x-ray scattering of MnO:L2,3 edge measurements and assessment of their interpretation

The resonant inelastic x-ray scattering _RIXS_ of MnO measured with high energy resolution across the L2,3 absorption edges of Mn is characterized by a very rich spectral structure due to the local electronic excitations. The spectra are dominated by dd and charge transfer excitations, both dipole allowed in the RIXS process. The spectra strongly depend on the energy and polarization of the incident photons. This vast experimental basis allows an accurate determination of the main parameters of theoretical models used to describe highly correlated electron systems like MnO. We show the results for the single impurity Anderson model and the single ion crystal field model and we compare them. Both models reproduce well the dd excitation spectrum, but the former can also predict satisfactorily the charge transfer excitations

Magnetic properties and orbital anisotropy driven bu Mn(2+) in nonstoichiometric La(x)MnO(3-delta) thin films

Magnetic properties and orbital anisotropy driven bu Mn(2+) in nonstoichiometric La(x)MnO(3-delta) thin film

Electronic structure of Cu-doped ZnO thin films by z-ray absorption, magneetic circular dichroism, and resonant inelastic x-ray scattering

Electronic structure of Cu-doped ZnO thin films by z-ray absorption, magneetic circular dichroism, and resonant inelastic x-ray scatterin

Multiple electronic-valence elements in A-site perovskite manganites: a route to high metallicity and an orbital order coexistence

With respect to the double-exchange hopping mechanism, the role of chemical element sitting at perovskite A-site (generally hosting an alkali-earth or a rare-earth atom) has always been considered as “silent,” being the corresponding conduction band of the A-site element too far from Fermi’s energy level. In order to make such an atomic site active within the transport mechanism, a possible strategy calls for a partial insertion of multiple-valence ions which also show the requested electronic properties (i.e. conduction band crossing EF). In manganites, the ideal candidate isindeed Mn-ions themselves. Here we show that a partial substitution of Mn ions at perovskite A-site (therefore named as A-site perovskite manganites) is indeed possible in both La-deficient LaxMnO3 and off-stoichiometric LaxSryMnO3 manganite thin films. By combining polarization-dependent x-ray absorption spectroscopy and resonant inelastic x-ray spectroscopy, the relevant Mn2+ content is demonstrated, and it is unambiguously assigned its crystallographic site (namely, the perovskite A-site). Similarly to traditional manganites, Mn2+ substitution induces the required Mn3+/Mn4+ mixed population. However, differently from the latter, the Mn2+ ions at perovskite A-site are electronically involved in the transport mechanisms, having their electronic bands crossing the Fermi energy. Such an energetic configuration favours the hopping of electrical charge through that site (usually silent), in addition to the traditional Mn3+/Mn4+ hopping path (named Multiple double-exchange mechanism), thus contributing to the ferromagnetic and metallic state. Furthermore, to an highly metallic and ferromagnetic state, it surprisingly corresponds also a strong Mn orbital order. Indeed, the tendency of the orbitals to order locally usually strongly compete with the kinetic energy of the free charge carriers, which however tends to destroy long range orbital order. Multiple double-exchange mechanism is here demonstrated that destroys such a dichotomy by sustaining the co-existence of highly metallic states with orbital ordered phase. This will open unexplored perspectives in both theoretical and experimental possibilities based on such a coexistence of spin/orbital order (generally in competition with each other), and more in general in fundamental studies on transport mechanism in strongly correlated electrons systems