  The correlation between the transport properties and structural degrees of
freedom of conducting polymers is a central concern in both practical
applications and scientific research. In this study, we demonstrated the
existence of mesoscopic two-dimensional (2D) coherent charge transport in
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film by
performing structural investigations and high-field magnetoconductance (MC)
measurements in magnetic fields of up to 15 T. We succeeded in observing marked
positive MCs reflecting 2D electronic states in a conventional drop-cast film.
This low-dimensional feature is surprising, since PEDOT:PSS-a mixture of two
different polymers-seems to be significantly different from crystalline 2D
materials in the viewpoint of the structural inhomogeneity, especially in
popular drop-cast thick films. The results of the structural experiments
suggest that such 2D transport originates from the nanometer-scale
self-assembled laminated structure, which is composed of PEDOT nanocrystals
wrapped by insulating sheets consisting of amorphous PSSs. These results
indicate that charge transport in the PEDOT:PSS film can be divided into two
regimes: mesoscopic 2D coherent tunneling and macroscopic three-dimensional
hopping among 2D states. Our findings elucidate the hieratical nature of charge
transport in the PEDOT:PSS film, which could provide new insight into a recent
engineering concern, i.e., the anisotropic conductance.
