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Metal-insulator crossover accompanied by the dual nature of 5$$f$$ electrons with localized and itinerant charancters in $$beta$$-US$$_2$$

Metoki, Naoto  ; Sakai, Hironori  ; Yamamoto, Etsuji ; Haga, Yoshinori ; Matsuda, Tatsuma; Ikeda, Shugo*

Magnetic excitation of a narrow gap semiconductor $$beta$$-US$$_2$$was studied by means of neutron scattering. At low temperatures clear crystalline electric field (CEF) excitations were observed, indicating localized character of 5$$f$$ electrons. The excitation energy $$sim$$7 meV of the pseudo doublet state is consistent with the level scheme based on 5$$f^2$$ configuration of U$$^ {4+}$$ ions, which reproduces the magnetic susceptibility, magnetization, and specific heat. With elevating temperature the conductivity recovers with 5$$f$$ carriers excited beyond the gap of 90 K. Simultaneously the CEF excitation becomes weak and broad, and is replaced by a quasi-elastic response of magnetic origin, indicating the crossover of 5$$f$$ character from localized to itinerant.

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Category:Physics, Multidisciplinary

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