Transition-edge sensors: achieving true potential

Summary

The 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 bolometers
2. 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 transition

An 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.

Impact Summary

There is likely to be significant IPR generated during the course of the grant and appropriate mechanisms are in place to facilitate exploitation of our work. Facilities for IP protection and exploitation are available through a subsidiary wholly owned by Lancaster University. We have already discussed potential impacts with Lancaster's Research and Enterprise division, who are our primary intellectual property arm and we will continue to work closely with them, meeting bi-annually throughout the grant to brief them on latest developments and review opportunities to develop IPR. The Lancaster Physics Department hosts a new Quantum Technology Centre (http://www.physics.lancs.ac.uk/qtc) with a full-time HEIF-funded Business Development Manager, who will provide additional advice and support for the development of our IP.

Since emerging applications include the nondestructive assay of nuclear materials for safeguards and fuel cycle applications, alpha-particle forensics, environmental monitoring of actinides, nuclear data measurements and the operational detection of nuclear materials, (e.g. at border crossings), the results of the proposed research directly address the needs summarized under the EPSRC Global Uncertainty theme. This project is of importance for the future development of at least two (Space and Sensor Systems) of the 10 candidate areas for the UK Technology and Innovation Centres (TICs), as discussed in the Technology Strategy Board's "Strategy and Implementation plan" (May, 2011, http://www.innovateuk.org/deliveringinnovation/technology-and-innovation-centres.ashx).
The new knowledge generated by the proposed project will accelerate in the first instance the development of TES-based detectors and be delivered to the LTD community through the interaction with many academic groups involved in TES and low-temperature detector development. We have established strong links with our Project Partners - Sensor and Research Technology Division of Netherlands Institute for Space Research (SRON), Centre of Astrobiology (CAB) in Spain and the National Institute of Standards and Technology in Boulder, Colorado (NIST). Such leading groups as NASA's Goddard Spaceflight Centre in Maryland (GSFC), and the National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, Japan, have expressed written interest and support our program. We are closely linked to a number of other centers worldwide through networks run by our Partners in different areas of TES development and also the KTN in low temperature detectors launched at the LTD14 conference in August 2011. The SRON-led consortia which develop the far-IR Safari instrument for the Spica mission and the X-ray XMS instrument for the Athena mission comprise in total well over 20 institutes worldwide, including RAL, MSSL, Cambridge and Cardiff University from the UK. The NIST network on Quantum Sensors involves many major institutes worldwide, including the UK Astronomy Technology Center, and the Universities of Edinburgh and Cardiff. We will be communicating directly with the UK KTN on Space and Sensors and Instrumentation.

The new understanding of energy deposition and loss in thin film structures will also have impact on emerging low-temperature detector technologies. The TES development is a central activity in the LTD community, which serves many surrounding communities involved in X-ray, optical interferometry, far IR, and sub-mm astronomy, dark-matter search, neutrino mass experiments, THz surveillance, quantum information processing, synchrotron science and its associated analytical chemical, biological and pharmaceutical communities, industrial material analysis, nuclear material analysis and safet