  We report on the high-pressure growth, structural characterization, and
investigation of the electronic properties of single-crystalline LaFeAsO
co-substituted by Sm and P, in both its normal- and superconducting states.
Here, the appearance of superconductivity is attributed to the inner chemical
pressure induced by the smaller-size isovalent substituents. X-ray structural
refinements show that the partial substitution of La by Sm and As by P in the
parent LaFeAsO compound leads to a contraction in both the conducting
Fe2(As,P)2 layers and the interlayer spacing. The main parameters of the
superconducting state, including the critical temperature, the lower- and upper
critical fields, as well as the coherence length, the penetration depth, and
their anisotropy, were determined from magnetometry measurements on a
single-crystalline La0.87Sm0.13FeAs0.91P0.09O sample. The critical current
density (jc), as resulting from loops of magnetization hysteresis in the
self-generated magnetic field, is 2 x 106 A/cm2 at 2 K. Overall, our findings
illustrate a rare and interesting case of how superconductivity can be induced
by co-substitution in the 1111 family. Such approach delineates new
possibilities in the creation of superconductors by design, thus stimulating
the exploration of related systems under multi-chemical pressure conditions.
