Author Affiliations

Luca Bergamini,^a,b Yudong Wang,^c Jeffrey M. Gaskell,^d Nerea Zabala,^a,b C. H. de Groot,^c David W. Sheel,^d Javier Aizpurua,^b and Otto L. Muskens^e

^aDepartment of Electricity and Electronics, FCT-ZTF, UPV-EHU, 48080 Bilbao, Spain

^bMaterials Physics Center, CSIC-UPV/EHU and DIPC, 20018 San Sebastian

^cNano Group, Faculty of Physical Sciences and Engineering, University of Southampton, Highfield, Southampton SO17 1BJ, UK

^dMaterials and Physics Research Centre, University of Salford, Manchester, M5 4WT, UK

^ePhysics and Astronomy, Faculty of Physical Sciences and Engineering, University of Southampton, Highfield, Southampton SO17 1BJ, UK