Four probe electrode structure for measurement

1. Semiconducting Polymers at High Carrier Densities: Nonlinear Transport in Agreement with Luttinger Liquid TheoryAlan J. Heeger, University of CA - Santa Barbara, DMR 0602280 FET data Four probe electrode structure for measurement of the gated nonlinear conductivity in polymer FETs In Luttinger’s model of the 1D metal, charge and spin are decoupled. The elementary excitations along the chain are collective oscillations of charge density and spin density, propagating coherently, but in general at different velocities. The transport properties of the correlated LL electronic state are described in terms of interaction-dependent power law correlations, I ~ Vβ at low temperatures and σ ~ T at low bias (I and V are current and voltage, respectively, and σ and T are temperature and conductivity, respectively), where +1 = β. Moreover, LL theory predicts the universality of all measured I-V curves at different temperatures onto a single master curve when I/T +1is plotted against eV/kBT, as described by the equation I = I0T+1·sinh(γeV/kBT)·|Γ((β+1)/2 + iγeV/πkBT)|2 (1) where kB is the Boltzmann constant, e is the electron charge, I0 and γ are constants independent of T and V, and Γ(x) is the gamma function. The exponents  and β are related to the tunnelling density of states. FET data scale onto a “universal” curve I-V data plotted as I/T1+vs. eVSD/kBT PBTTT for VG = -160V (α = 4.36, β = 5.26). Solid curve is best fits to Eqn. 1. The nonlinear transport data obtained from PBTTT at relatively high carrier densities are in agreement with the predictions of the Luttinger Liquid theory. The data obtained using a wide range of parameters (temperature, gate-induced carrier density, source-drain voltage and doping level) scale onto the universal curve predicted for transport in systems with electronic structure described by the Luttinger Liquid model. Variation of the charge density in the channel via gating confirmed the existence of the LL electronic state. J.D.Yuen et al. Nature Materials, 8, 572 (2009)

2. Semiconducting Polymers at High Carrier Densities: Nonlinear Transport in Agreement with Luttinger Liquid TheoryAlan J. Heeger, University of CA - Santa Barbara, DMR 0602280 • Outreach • Thin film transistors (TFTs) fabricated from semiconducting polymers continue to be of interest as components of low-cost and printable plastic electronic circuits. Integration of organic TFTs into LCD, OLED or EPD arrays leading to all-plastic displays would significantly reduce fabrication costs. • Professor Heeger has given invited (Keynote and Plenary) lectures on the results of this research at conferences in the United States, Europe and Asia. • In the “News and Views” article in the same issue of Nature Materials, [Vol.8, 572 (2009)], A. Troisi commented, that based upon our results, generalization of Luttinger Liquid Theory may be possible and that “Such generalization could be the key to achieving a coherent description of the electric properties of organic conductors”. Education This is a classic interdisciplinary study involving a combination of physics, chemistry, materials science and device science. The authors include graduate students in the Materials Department (J.D. Yuen) and the Physics Department (N.E. Coates); they collaborated with post-doctoral researchers whose previous research background is in Physics. The polymer semiconductors are materials from Chemistry. Hundreds of papers have been published on Field Effect Transistors fabricated with semiconducting polymers as the material in the channel. Typically, such papers report the I-V curves and infer a carrier mobility. To our knowledge, this is the first publication where the transport mechanism is specifically addressed.