Complex Microwave Conductivity of Na-DNA Powders

We report the complex microwave conductivity, σ=σ₁-iσ₂, of Na-DNA powders, which was measured from 80 K to 300 K by using a microwave cavity perturbation technique. We found that the magnitude of σ₁ near room temperature was much larger than the contribution of the surrounding water molecules, and that the decrease of σ₁ with decreasing temperature was sufficiently stronger than that of the conduction of counterions. These results clearly suggest that the electrical conduction of Na-DNA is intrinsically semiconductive.