Tuning the Conductivity by Disorder and Electric Field Near the Metal–Insulator Transition

The electric field-dependent conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) [PEDOT:PSS], from metallic to insulator, is investigated in a temperature range of 4.2–200 K. The conductivity of PEDOT:PSS is systematically varied from 36 to 1070 S/cm, with the addition of dimethyl sulfoxide (DMSO) and ethylene glycol (EG). As the delocalization increases, the onset of increase in conductivity occurs at lower fields. The field-dependent conductivity fits to a power law, and the values of the field-induced delocalization length (LE) are estimated. LE increases at low temperatures for metallic samples and decreases for insulators. The data for all samples collapse onto the scaling function fit at all temperatures. This scaling fit shows that the field enhances the correlated transport among delocalized states and increases the conductivity. The J/T1+α vs eV/kBT analysis for metallic and critical samples collapses onto a straight line fit, and it deviates for the insulating sample.