Angew. Chem. Int. Ed. (2012)

A small amount of chemical doping induces superconductivity — electrical conduction with zero resistivity — in certain cuprate oxides. The degree and chemical nature of the doping species controls the number of charge carriers introduced in the material, as well as the critical temperature (Tc) below which superconductivity behaviour is observed. However, the amount of chemical doping must be set beforehand, during the preparation step.

Yoram Dagan and colleagues at Tel-Aviv University and the Shanghai Institute of Materia Medica have now found that it is possible to modulate the number of charges in cuprate superconductor films by depositing a self-assembled monolayer on their surface. The monolayer is made of light-sensitive polar compounds, such as an azobenzene derivative, or nanostructures, such as a porphyrin–nanotube composite. On irradiation with light, charges are transferred from the cuprate oxide to the monolayer, resulting in a hole-doped superconductor with a different Tc. The process is reversed when the light is switched off.

Although the effect is relatively small — amounting to about 2 K difference in Tc — the study clearly demonstrates that functional self-assembled monolayers can be used to control the Tc of superconductive cuprate oxides. The effect could be exploited to make dissipationless electrical switches or functional devices for memory storage.