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تسجيل مستخدم جديدOptical and photoelectrical studies on anisotropic metal-insulator transition of RuAs
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The anisotropic changes in the electronic structure of a metal-to-insulator transition (MIT) material, RuAs, with two-step phase transition are reported by using polarized optical conductivity [$sigma(omega)$] spectra, angle-integrated photoelectron (PE) spectra, and band calculations based on local density approximation (LDA). Both the PE and $sigma(omega)$ spectra not only in the high-temperature (HT) phase but also in the low-temperature (LT) phase as well as the energy gap formation owing to the MIT were almost consistent with those derived from the LDA band calculations, so the fundamental electronic structure in the HT and LT phases can be explained without electron correlations. However, the electronic structure in the middle phase between the HT and LT phases has not been clarified. The polarized $sigma(omega)$ spectra revealed not only the anisotropic energy gap formation but also the anisotropic gap-opening temperature, i.e., the energy gap along the $c$ axis in the HT phase starts to open near the higher transition temperature, but that along the $b$ axis opens below the lower transition temperature. The finding suggests that the two-step MIT originates from the anisotropic energy gap formation.
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The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below
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