ICMAB (Barcelona) and ICMA (Zaragoza) offer one PhD position in the framework of the project "X-ray detectors based on Transition-Edge Sensors: optimization of a pixel and development of arrays”. The PhD thesis will aim at characterizing the detectors, performing electrothermal modeling and studying the physics behind the superconducting transition.

Radiation detectors based on superconductors and working at cryogenic temperatures, close to the absolute zero temperature, constitute a new generation of devices essential for Big Science (Astrophysics, Cosmology, ...) as well as for nanotechnology and quantum technologies. As examples, they are installed in several large telescopes and will constitute, the detector of the high resolution spectrometer onboard the next X-ray telescope of the European Space Agency (ESA), Athena, to be launched in 2032 (see for instance ref. [3]).

The group constituted by scientists of ICMA and ICMAB is developing Transition-Edge Sensors [1,2] for X-ray astronomy or Dark Matter search, among other applications. It is funded by the Spanish MICINN,  the European Commission, and ESA.

Transition-Edge Sensors are extremely sensitive microcalorimeters, and constitute the forefront of these new generation devices. In spite of the huge improvement of performances and progress in understanding the physics governing them, there remain still several open questions, essential to further optimize them and thus approach their resolution to the fundamental theoretical limits. The two most relevant issues are the nature of the superconducting transition (i.e., the physical mechanism responsible for the appearance of resistivity in the devices) and the origin of a so-called excess or unexplained noise. To gain knowledge on the latter, a suitable electrothermal modeling of the detectors is important.

    

The goal of the thesis will be to characterize TES-based detectors in a dilution cryostat, at temperatures between 50 and 100mK. Characterization includes I-V curves, complex impedance and noise measurements, as well as detection of single photons from a X-ray source. Electrothermal modeling will be used to reproduce the complex impedance and noise data. Analyses of the device parameters as a function of design and operation parameters will be used to optimize them and to discriminate between transition mechanisms. Special attention will be paid to the possible role of vortex motion (Berezinskii-Kosterlitz-Thouless transition) and to the long range proximity effects and derived weak link behaviour (see refs. [2,4] for details).

The student will work in Zaragoza (ICMA) or Barcelona (ICMAB), within a multidisciplinary team constituted by experts in materials science, superconductivity, nanotechnology, cryogenics and engineering; he/she will get familiar also with several of the above mentioned applications.

To apply

We are looking for a PhD candidate with background in physics or electrical engineering, highly motivated and interested in multidisciplinar projects. Knowledge in Solid State Physics, Superconductivity, Cryogenics and use of Matlab and similar is not specifically required but will be valued.

Interested candidates should email Dr. Lourdes Fàbrega (This email address is being protected from spambots. You need JavaScript enabled to view it.) or Dr. Agustín Camón (This email address is being protected from spambots. You need JavaScript enabled to view it.), including:

• A personal motivation letter
• Your CV

Supervisors

• Dr. Lourdes Fàbrega, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)
• Dr. A.Camón, Instituto de Ciencia de Materiales de Aragón (ICMA-CSIC)

Projects

• "X-ray detectors based on Transition-Edge Sensors: optimization of a pixel and development of arrays” (Athena18-TES)  (RTI2018-096686-B-C22)
• “Integrated Activities for the High Energy Astrophysics Domain” (AHEAD2020, just awarded within H2020-INFRAIA-2018-2020 call).

References

1. K. D. Irwin and C.C. Hilton, "Transition-Edge Sensors in Cryogenic Particle Detection”, edited by C. Enss, Springer-Verlag, Berlin Heidelberg, Topics in Applied Physics, vol. 99 pp. 63–149 (2005).
2. “Review of superconducting transition-edge sensors for x-ray and gamma-ray spectroscopy”, J.N. Ullom, D.A.Bennett, Supercond. Sci. Technol. 28, 084003 (2015)
3. L. Fàbrega, A.Camón, J.L.Costa-Krämer, C.Pobes, M.Parra-Borderías, I.Fernández-Martínez, R.Jáudenes, P.Cereceda, M.T.Ceballos, X.Barcons, J.Sesé, J.Martín-Pintado, L.Gottardi, M.Bruijn, M.Jambunathan, R.H. den Hartog, J. van der Kuur, J.W.den Herder, D.Barret , “Towards Mo/Au based TES detectors for Athena/X-IFU”, SPIE Proceed. Series 9144, 91445P (2014)
4. L.Fàbrega, A.Camón, P.Strichovanec, C.Pobes, R.González-Arrabal, “Large current-induced broadening of the superconducting transition in Mo/Au TES”, Supercond. Sci. Technol. 32, 015006 (2019)

Download here the call in SPANISH and ENGLISH.