The surface of Sr2Ru0.9Mo0.1O4: a LEED and STM study

In the unconventional superconductor Sr2RuO4, substitution of a small amount of Mo for Ru destroys the superconducting state. We have used low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to study the cleaved (1 0 0) surface of the Mo-doped strontium ruthenate: Sr2Ru0.9Mo0.1O4. Excellent LEED patterns indicate a well-ordered surface similar to Sr2RuO4. The analysis of LEED-I(V) spectra revealed that the (Ru/Mo)O6 octahedra at the surface are rotated alternating clockwise and counterclockwise by 8.8° ± 2.5° about the direction of the surface normal, which is identical to these on the surface of Sr2RuO4. But the high-resolution STM images of Sr2Ru0.9Mo0.1O4 show a surface fundamentally different from that of Sr2RuO4. The STM images are surprisingly inhomogeneous without clear atomic resolution. This indicates a local spatial roughness in the electronic structure induced by the Mo doping.