  Devices based on a pure spin current (a flow of spin angular momentum) have
been attracting increasing attention as key ingredients for low-dissipation
electronics. To integrate such spintronics devices into charge-based
technologies, an electric detection of spin current is essential. Inverse spin
Hall effect converts a spin current into an electric voltage through spin-orbit
coupling. Noble metals such as Pt and Pd, and also Cu-based alloys, owing to
the large direct spin Hall effect, have been regarded as potential materials
for a spin-current injector. Those materials, however, are not promising as a
spin-current detector based on inverse spin Hall effect. Their spin Hall
resistivity rho_SH, representing the performance as a detector, is not large
enough mainly due to their low charge resistivity. Here we demonstrate that
heavy transition metal oxides can overcome such limitations inherent to
metal-based spintronics materials. A binary 5d transition metal oxide IrO2,
owing to its large resistivity as well as a large spin-orbit coupling
associated with 5d character of conduction electrons, was found to show a
gigantic rho_SH ~ 38 microohm cm at room temperature, one order of magnitude
larger than those of noble metals and Cu-based alloys and even comparable to
those of atomic layer thin film of W and Ta.
