Nonlinearity exponents in lightly doped Conducting Polymers

TL;DR

This study investigates the nonlinear electrical behavior of various conducting polymers, revealing a universal scaling law characterized by a nonlinearity exponent, and demonstrates the applicability of a tunneling model over a wide range of conditions.

Contribution

It introduces a phenomenological scaling analysis to extract a nonlinearity exponent in conducting polymers, linking electric field onset to conductivity, and applies a tunneling model to describe the data.

Findings

Existence of a single electric field scale in all systems.

The nonlinearity exponent varies between -0.5 and 0.75.

Field-dependent data fit the Glatzman-Matveev tunneling model over nine orders of magnitude.

Abstract

The \textit{I-V} characteristics of four conducting polymer systems like doped polypyrrole (PPy), poly 3,4 ethylene dioxythiophene (PEDOT), polydiacetylene (PDA) and polyaniline (PA) in as many physical forms have been investigated at different temperatures, quenched disorder and magnetic fields. Transport data clearly confirm the existence of a \textit{single} electric field scale in any system. Based upon this observation, a phenomenological scaling analysis is applied, leading to extraction of a concrete number $x_M$, called nonlinearity exponent. The latter serves to characterize a set of \textit{I-V} curves. The onset field $F_o$ at which conductivity starts deviating from its Ohmic value $\sigma_0$ scales as $F_o \sim \sigma_0^{x_M}$. Field-dependent data are shown to be described by Glatzman-Matveev multi-step tunneling model [JETP 67, 1276 (1988)] in a near-perfect manner over nine orders of magnitude in conductivity and five order of magnitudes in electric field. $x_M$ is found to possess both positive and negative values lying between -1/2 and 3/4. There is no theory at present for the exponent. Some issues concerning applicability of the Glatzman-Matveev model are discussed.