In the hole-doped cuprates, a small number of carriers suppresses antiferromagnetism and induces superconductivity. In the electron-doped cuprates, on the other hand, superconductivity appears only ...in a narrow window of high-doped Ce concentration after reduction annealing, and strong antiferromagnetic correlation persists in the superconducting phase. Recently, Pr(1.3-x)La0.7Ce(x)CuO4 (PLCCO) bulk single crystals annealed by a protect annealing method showed a high critical temperature of around 27 K for small Ce content down to 0.05. Here, by angle-resolved photoemission spectroscopy measurements of PLCCO crystals, we observed a sharp quasi-particle peak on the entire Fermi surface without signature of an antiferromagnetic pseudogap unlike all the previous work, indicating a dramatic reduction of antiferromagnetic correlation length and/or of magnetic moments. The superconducting state was found to extend over a wide electron concentration range. The present results fundamentally challenge the long-standing picture on the electronic structure in the electron-doped regime.
Structural phase separation in AxFe2-ySe2 system has been studied by different experimental techniques, however, it should be important to know how the electronic uniformity is influenced, on which ...length scale the electronic phases coexist, and what is their spatial distribution. Here, we have used novel scanning photoelectron microscopy (SPEM) to study the electronic phase separation in KxFe2-ySe2, providing a direct measurement of the topological spatial distribution of the different electronic phases. The SPEM results reveal a peculiar interconnected conducting filamentary phase that is embedded in the insulating texture. The filamentary structure with a particular topological geometry could be important for the high Tc superconductivity in the presence of a phase with a large magnetic moment in AxFe2-ySe2 materials.
We have investigated electronic structure evolution by cation substitution in Ba 3 − x Sr x Nb5 O15 by means of hard x-ray photoemission spectroscopy. Localization of Nb 4 d electrons manifests as ...spectral weight transfer from a coherent component at the Fermi level to an incoherent one at 1–2 eV below it. This behavior is similar to that of electron-doped SrTiO3 . On the other hand, Nb 3 d and 4 p core level spectra exhibit a screening effect with an energy scale of 1–2 eV by the coherent Nb 4 d electrons similar to 4 d electron systems near Mott transitions. The energy scale indicates that electron correlation is involved in the metal to insulator transition in the present system, although the Nb 4 d band is about 1/10 filled. The present results suggest a mechanism of electron localization due to atomic disorder and electron correlation.
We have studied the electronic structure of Ba1−xSrxV13O18 (x=0,0.2,1) at different temperatures across the trimerization and charge-order transitions using hard x-ray photoemission spectroscopy ...(HAXPES). The V 2p HAXPES indicates V2+/V3+ charge order and fluctuation in the high-temperature tetramer phase, low-temperature trimer phase, and intermediate-temperature charge-order phase in the series of x=0,0.2,1. In the valence-band HAXPES, although the spectral weight at the Fermi level tends to be suppressed in all the phases due to strong charge order or fluctuation, it increases in the trimer phase at x=0.2, in agreement with the decrease of resistivity and the increase of itinerant electrons in the trimer phase. Interestingly, in the most conducting x=1 without the charge-order phase, the spectral weight at the Fermi level is strongly suppressed even in the trimer phase, indicating that charge fluctuation in the trimer phase is different between x=0.2 and 1.
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