Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA hard X- ray probe to study doping-dependent electron redistribution and strong covalency in La_{1-x}Sr_{1+x}MnO_4
101
0
0.0
(
0
)
Added by
Javier Herrero-Martin
Publication date
2009
fields
Physics
and research's language is
English
Authors
Javier Herrero-Martin
Ask ChatGPT about the research
No Arabic abstract
The effect of doping on the electronic structure at the Mn sites in the La_{1-x}Sr_{1+x}MnO_4 series (x=0, 0.3 and 0.5) was studied by means of non-resonant hard X- ray emission spectroscopy (XES). We observe a linear dichroism in the Mn K-beta main lines (3p to 1s transitions) that is strongest for x=0 and decreases with increasing x to 0.5. The Mn K-beta main lines in the poly-crystalline samples change considerably less upon increasing the hole doping (substitution of La by Sr) than it would be expected based on the change of formal valence. From this we conclude that the charge and spin density at the Mn sites are only little affected by doping. This implies that holes injected in the La_{1-x}Sr_{1+x}MnO_4 series mainly result in a decrease of charge density on the oxygen atoms, i.e. oxygen takes part in the charge balancing. These findings are supported by many-body cluster calculations.
rate research
Read More
We present the electronic structure of Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution photoemission spectroscopy. In the vicinity of Fermi level, it was found that the electronic structure were composed of a Cr 3d local state with the t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.
By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La_{1-x}Sr_{x}MnO_{3} as a function of x. In the Mn 2p_{3/2} HX-PES spectra, we observed the shoulder structure due to the Mn^{3+} well-screened state. However, the intensity at x=0.8 was too small to explain its higher electrical conductivity than x=0.0, which confirms our recent analysis on the Mn 2p_{3/2} XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight.
We study long wavelength magnetic excitations in lightly doped La_{2-x}Sr_{x}CuO_{4} (x < 0.03) detwinned crystals. The lowest energy magnetic anisotropy induced gap can be understood in terms of the antisymmetric spin interaction inside the antiferromagnetic (AF) phase. The second magnetic resonace, analyzed in terms of in-plane spin anisotropy, shows unconventional behavior within the AF state and led to the discovery of collective spin excitations pertaining to a field induced magnetically ordered state. This state persists in a 9 T field to more than 100 K above the N{e}el temperature in x = 0.01.
A laboratory hard X-ray photoelectron spectroscopy (HXPS) system equipped with a monochromatic Cr K$alpha$ ($h u = 5414.7$ eV) X-ray source was applied to an investigation of the core-level electronic structure of La$_{1-x}$Sr$_x$MnO$_3$. No appreciable high binding-energy shoulder in the O $1s$ HXPS spectra were observed while an enhanced low binding-energy shoulder structure in the Mn $2p_{3/2}$ HXPS spectra were observed, both of which are manifestation of high bulk sensitivity. Such high bulk sensitivity enabled us to track the Mn $2p_{3/2}$ shoulder structure in the full range of $x$, giving us a new insight into the binding-energy shift of the Mn $2p_{3/2}$ core level. Comparisons with the results using the conventional laboratory XPS ($h u = 1486.6$ eV) as well as those using a synchrotron radiation source ($h u = 7939.9$ eV) demonstrate that HXPS is a powerful and convenient tool to analyze the bulk electronic structure of a host of different compounds.
The microscopic details of flux line lattice state studied by muon spin rotation is reported in an electron-doped high-$T_{rm c}$ cuprate superconductor, Sr$_{1-x}$La$_{x}$CuO$_{2}$ (SLCO, $x=0.10$--0.15). A clear sign of phase separation between magnetic and non-magnetic phases is observed, where the effective magnetic penetration depth [$lambdaequivlambda(T,H)$] is determined selectively for the latter phase. The extremely small value of $lambda(0,0)$ %versus $T_{rm c}$ and corresponding large superfluid density ($n_s propto lambda^{-2}$) is consistent with presence of a large Fermi surface with carrier density of $1+x$, which suggests the breakdown of the doped Mott insulator even at the optimal doping in SLCO. Moreover, a relatively weak anisotropy in the superconducting order parameter is suggested by the field dependence of $lambda(0,H)$. These observations strongly suggest that the superconductivity in SLCO is of a different class from hole-doped cuprates.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
