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Impact of atomic defects in the electronic states of FeSe(1-x)Sx superconducting crystals

Yanina Fasano

Prof. Dr. Yanina Fasano has received her PhD in Physics from the Instituto Balseiro at Patagonia, Argentina, in 2003. After a postdoctoral appointment at the University of Geneva, Switzerland, she joined the Low Temperatures Lab at the Centro Atómico Bariloche of the Atomic National Commission as a permanent researcher of Conicet. In 2021 she became assistant professor at the Instituto Balseiro. Her research is in the field of experimental condensed matter at low temperatures, focusing on superconductivity and vortex matter. She received the Houssay prize of the Ministry of Science, Technology and Innovation of Argentina in 2022 and was honored with the Georg Forster Research Prize from the Alexander von Humboldt Foundation in 2021.


The electronic properties of Fe-based superconductors are drastically affected by deformations on their crystal structure introduced by doping and pressure. Here we study single crystals of  FeSe1-xSx and reveal that local crystal deformations such as atomic-scale defects impact the spectral shape of the electronic core level states of the material.  By means of scanning tunnelling microscopy (STM) we image S-doping induced defects as well as diluted dumbbell defects associated with Fe vacancies. We have access to  the electronic structure of the samples by means of X-ray photoemission spectroscopy (XPS) and show that the spectral shape of the Se core levels can only be adequately described by considering a principal plus a minor component of the electronic states. We find this result for both pure and S-doped samples, irrespective  that in the latter case the material presents extra crystal defects associated to doping with S atoms. We argue that the second component in our XPS spectra is associated with the ubiquitous dumbbell defects in FeSe that are known to entail a significant modification of the electronic clouds of surrounding atoms. We further support these findings by means of DFT calculations. Work partially published in  J. Phys. Mater. 5 044008 (2022)   J. Phys. Mater. 5 044008