Light-induced superconductivity using a photoactive electric double layer

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Science  13 Feb 2015:
Vol. 347, Issue 6223, pp. 743-746
DOI: 10.1126/science.1256783

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Light switch for superconductivity

The conducting properties of materials sensitively depend on the available carrier concentration. Physicists can vary this concentration by inducing carriers in the material; for example, by placing it next to an ionic liquid in an electric field. Suda et al. instead used a layer of the molecule spiropyran, which changes from a non-ionic to an ionic form when it is irradiated by ultraviolet (UV) light. The authors placed the layer on top of a thin crystal of an organic material. When they shone UV light on the spiropyran, the adjacent material became superconducting, thanks to the carriers induced at the interface.

Science, this issue p. 743


Electric double layers (EDLs) of ionic liquids have been used in superconducting field-effect transistors as nanogap capacitors. Because of the freezing of the ionic motion below ~200 kelvin, modulations of the carrier density have been limited to the high-temperature regime. Here we observe carrier-doping–induced superconductivity in an organic Mott insulator with a photoinduced EDL based on a photochromic spiropyran monolayer. Because the spiropyran can isomerize reversibly between nonionic and zwitterionic isomers through photochemical processes, two distinct built-in electric fields can modulate the carrier density even at cryogenic conditions.

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