Figure 2: Electrical properties of two-dimensionally doped La2CuO4 superlattices.
In a, a sketch of the structure is represented. Starting from the La2CuO4 structure, superlattices are formed by regularly replacing single layers of LaO with SrO planes. The general formula can be written as: [SrO-LaO-CuO2+N × (LaO-LaO-CuO2)] × R. The periodicity N is defined as the number of spacing blocks between two SrO-containing blocks, whereas R indicates the number of superlattice units. (b) Representative in-plane resistivity measurements for superlattices with different spacing N, epitaxially grown along the c-direction on LaSrAlO4 (001) substrates. Each spacing is marked with a different colour as defined in c, in which the solid square symbols represent the value of the critical temperature Tc plotted as a function of N. Here the error bars show the s.d. of the Tc values obtained for a set of samples having the same composition. For those compositions (value of N), in which a set of two samples was considered for the determination of the average critical temperature, both Tc data points are shown in the diagram (open square symbols). The uncertainty in the definition of the Tc value can be ascribed to normal sample-to-sample variations due to, for example, light stoichiometry offset, substrate roughness and strain.
