DOUBLING THE CRITICAL-TEMPERATURE OF LA1.9SR0.1CUO4 USING EPITAXIAL STRAIN

The discovery(1) of high-temperature superconductivity in copper oxide s raised the possibility that superconductivity could be achieved at r oom temperature. But since 1993, when a critical temperature (T-c) of 133 K was observed in the HgBa2Ca2Cu3O8+delta (ref. 2), no further pro gress has been made in raising the critical temperature through materi al design. It has been shown, however, that the application of hydrost atic pressure can raise T-c-up to similar to 164 K in the case of HgBa 2Ca2Cu3O8+delta (ref. 3). Here we show by analysing the uniaxial strai n and pressure derivatives of T-c, that compressive epitaxial strain i n thin films of copper oxide superconductors could in principle genera te much larger increases in the critical temperature than obtained by comparable hydrostatic pressures. We demonstrate the experimental feas ibility of this approach for the compound La1.9Sr0.1CuO4, where we obt ain a critical temperature of 49 K in strained single-crystal thin fil ms-roughly double the bulk value of 25 K. Furthermore, the resistive b ehaviour at low temperatures (but above T-c) of the strained samples c hanges markedly, going from insulating to metallic.