Thin films based on melanin are prepared and characterized. The films display electrical conductivities comparable with amorphous silicon as well as a host of other interesting and potentially useful optoelectronic properties. The results may be useful for melanin‐based applications such as chemi‐sensors (in a variety of architectures including OFETS with chemi‐sensitive channels) and bolometric photon detectors.

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The order of the vortex state in La1.9Sr0.1CuO4 is probed using muon-spin rotation and small-angle neutron scattering. A transition from a Bragg glass to a vortex glass is observed, where the latter is composed of disordered vortex lines. In the vicinity of the transition the microscopic behavior reflects a delicate interplay of thermally induced and pinning-induced disorder.

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The vortex glass state formed by magnetic flux lines in a type-II superconductor is shown to possess non-trivial three-body correlations. While such correlations are usually difficult to measure in glassy systems, the magnetic fields associated with the flux vortices allow us to probe these via muon-spin rotation measurements of the local field distribution. We show via numerical simulations and analytic calculations that these observations provide detailed microscopic insight into the local order of the vortex glass and more generally validate a theoretical framework for correlations in glassy systems.PACS numbers: 74.25. Qt, 76.75.+i, 61.20.Gy In systems which possess long range order, such as atomic crystals, the local arrangement of particles is easily obtained from scattering experiments. In disordered systems, the average correlation between the positions of two particles can be measured by scattering techniques, but inferring anything more about the local geometry is a far more subtle issue. Little is known experimentally about correlation functions of higher order. Measurements of three-body correlation functions for colloids imaged in a quasi-two-dimensional geometry have been reported recently [1]. However, bulk measurements of three-body correlation functions in any system are still unavailable and our understanding of such correlations derives mainly from simulations. This Letter reports a study of the local structure of the vortex glass phase in a bulk type-II superconductor. The vortex glass phase provides an example of a glassy system where the local geometry in the bulk is uniquely amenable to investigation, due to the magnetic fields associated with the vortices, which we measure by the muon-spin rotation (µSR) technique. By coupling these measurements with Monte Carlo simulations and analytic calculations, we demonstrate both the existence of non-trivial three-body correlations in the flux-line array and a theoretical framework in which they may be understood.In the mixed state of a type-II superconductor, an applied magnetic field penetrates as lines of magnetic flux, quantized in units of the flux quantum Φ 0 = h/2e. Such vortex lines would form an Abrikosov flux lattice at low temperatures in the absence of quenched disorder. As the temperature or the strength of disorder is increased, ordered arrangements of vortex lines yield to disordered ones [2,3]. Weak quenched disorder converts the crystal into a "Bragg glass" with quasi-long range order in translational correlations [4]. At stronger disorder, "vortex glass" states with short-ranged correlations are obtained. Neutron scattering measurements support the proposal of a power-law decay of translational correlations in the Bragg glass phase [5]. In contrast, structure and correlations in vortex glasses remain little understood.Our experimental system is La 1.9 Sr .1 CuO 4−δ (LSCO), an underdoped high-T c superconductor with properties which amplify the effects of thermal fluctuations and quenched disorder. It was recently shown using µS...