Transition-edge sensors: achieving true potential

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SummaryThe proposal is primarily a theoretical project aimed at resolving several of the most important outstanding problems associated with a promising type of cryogenic detector, the superconducting Transition Edge Sensor (TES), which offers unique capabilities far exceeding that of traditional semiconductor technology. Over the past decade TES-based detectors have found application in diverse areas from dark matter searches, X-ray astrophysics, time-resolved X-ray absorption spectroscopy, quantum information processing, biological sensors, industrial material analysis and homeland security. Practical instruments require a complex optimization of speed, linearity, energy resolution and array size. However, lack of understanding of the superconducting transition in TESs limits our ability to optimise performance and predict the behaviour of a new detector designs. The present models of TESs have played an important role during a period of extensive development of technology. However, based on empirical observations the models lack knowledge of the fundamental details of superconductivity, which determine the transition, and ultimately the performance of TESs. They cannot explain the observable energy resolution, and such fundamental properties as recently-discovered weak superconductivity of TESs. As a result, the current development path of TES detector for a certain applications is still very time consuming and costly, being in many aspects based on trial and error. Significant advances are expected if better understanding of the fundamental physics of TESs is achieved, because this would underpin accurate and streamlined design processes, leading to shorter periods of experiments with targeted design options.The project aims to develop new a theoretical model of the resistive transition in TESs based on fundamental superconductivity theory. The objectives are: 1. Understanding the mechanisms of the resistive transition in TESs as spatially inhomogeneous superconducting systems, simulating electrical and thermal fluctuations, which determine the energy resolution of TES micro- and nano- calorimeters and noise performance of bolometers2. Developing a model of non-local energy transport in multilayered TES structures, including energy escape and fluctuations over the extremely short time scale of energy deposition and down-conversion.3. stimulating the development of the next generation of high-performance TESs by evaluating the potential of graphene and few-layer boron nitride for engineering the coupling to a thermal bath and shaping the resistive transitionAn expected outcome of this project is a new approach to complex optimization of speed, linearity, energy resolution and array size for individual applications. A few examples illustrate the potential impact. An improvement of the energy resolution of TES-based soft X-ray detectors below 2 eV will allow the Athena X-ray mission proposal to ESA to study turbulence in the hot gas of clusters of galaxies, and will also allow the mapping of chemical shifts in X-ray fluorescence signals in Transmission Electron Microscopy (TEM), thus opening exciting possibilities for Industrial Materials Analysis. An increase in the number of pixels per array would lead to efficient imaging on a future X-ray telescope, and also provides the ability to sustain higher flux levels in emerging synchrotron applications, such as time-resolved X-ray spectroscopy. With several potential markets for high-resolution X-ray spectroscopy equipment, most notably synchrotron facilities and manufacturers of TEM equipment, the emergence of new companies is a likely consequence. For gamma-ray and neutron spectroscopy, larger arrays of TES detectors with higher energy resolution imply more efficient and faster screening, facilitating assessment tasks in such fields as non-destructive assay of spent nuclear fuel, and the operational detection of nuclear materials.