Superconductor–insulator transition in La2 − xSr x CuO4 at the pair quantum resistance

The superconductivity transition High-temperature superconductivity in copper oxides arises when a parent insulator compound is 'doped' by adding or removing valence electrons, usually by inserting atoms into the lattice structure. This would be better achieved by tuning the carrier density using the electric field effect, as it removes ambiguity about whether the electronic properties change because of alterations in the crystal structure or in the electronic structure. Such tuning is difficult to achieve because it requires perfect, ultrathin films and a huge local field. Bollinger et al. report the synthesis of one-cell-thick epitaxial films of La2xSrxCuO4, and the use of the films to make double-layer transistors. The transistors have very large fields, and by changing the surface carrier density, the critical temperature can be shifted by up to 30 K. The resistance varies as predicted for a two-dimensional superconductor–insulator transition.