Effects of x-ray irradiation on the crystal structure and the electrical resistance were examined at low temperatures for the insulating phase of spinel compound CuIr2S4. We found that the resistance decreases by more than five decades by irradiation at 8.5 K. The structural change from triclinic to tetragonal was observed at the same time. The x-ray-induced conductance is deduced to result from the destruction of Ir4+ dimers formed in the insulating phase. Slow relaxation of the resistance in the x-ray-induced state is also reported.
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