Hole-induced insulator-to-metal transition in La1-xSrxCrO3 epitaxial filmse

Article

关键词: RAY-ABSORPTION-SPECTROSCOPY;    CHEMICAL-POTENTIAL SHIFT;    AUGMENTED-WAVE METHOD;    OXIDE FUEL-CELLS;    ELECTRONIC-STRUCTURE;    MOTT-INSULATOR;    PHOTOEMISSION;    TEMPERATURE;    OXIDATION;    CHROMITE;   

DOI  :  10.1103/PhysRevB.91.155129

来源: SCIE

【 摘 要 】

We have investigated the evolution of the electronic properties of La1-xSrxCrO3 (0 <= x <= 1) epitaxial films deposited by molecular beam epitaxy (MBE) using x-ray diffraction, x-ray photoemission spectroscopy, Rutherford backscattering spectrometry, x-ray absorption spectroscopy, electrical transport, and ab initio modeling. LaCrO3 is an antiferromagnetic insulator, whereas SrCrO3 is a metal. Substituting Sr2+ for La3+ in LaCrO3 effectively dopes holes into the top of valence band, leading to Cr4+ (3d(2)) local electron configurations. Core-level and valence-band features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward the valence band maximum. The material becomes a p-type semiconductor at lower doping levels and an insulator-to-metal transition is observed at x >= 0.65, but only when the films are deposited with in-plane compression via lattice-mismatched heteroepitaxy. Valence-band x-ray photoemission spectroscopy reveals diminution of electronic state density at the Cr d t(2g) -derived top of the valence band, while O K-edge x-ray absorption spectroscopy shows the development of a new unoccupied state above the Fermi level as holes are doped into LaCrO3. The evolution of these bands with Sr concentration is accurately captured using density functional theory (DFT) with a Hubbard U correction of 3.0 eV (DFT + U). Resistivity data in the semiconducting regime (x <= 0.50) do not fit perfectly well to either a polaron hopping or band conduction model but are best interpreted in terms of a hybrid model. The activation energies extracted from these fits are well reproduced by DFT + U.

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