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Abstract:
Mixed-valent Rb4O6 provides an exceptional prototype material for
studying the interplay between local correlations (Hubbard U) and
electron kinetic energy (W) in the open sp-electron shell. Based on a
first-principles calculation we show that depending on U/W ratio, when
tuned by external pressure, Rb4O6 exhibits a surprising sequence of
phase transitions between strongly correlated antiferromagnetic
insulator, ferromagnetic insulator (U/W >> 1), moderately correlated
ferromagnetic half-metal (U/W similar to 1), and finally itinerant
nonmagnetic metal (U/W << 1). This sequence, which is counterintuitive
to the usual Bethe-Slater scenario, in addition exhibits the fully
spin-polarized half-metallic ferromagnetic state revealed within the
insulator-metal transition regime.
