Manifestations of broken symmetry:: The surface phases of Ca2-xSrxRuO4

The surface structural phases of Ca(2-x)Sr(x)RuO(4) are investigated using quantitative low energy electron diffraction. The broken symmetry at the surface enhances the structural instability against the RuO(6) rotational distortion while diminishing the instability against the RuO(6) tilt distortion occurring within the bulk crystal. As a result, suppressed structural and electronic surface phase transition temperatures are observed, including the appearance of an inherent Mott metal-to-insulator transition for x=0.1 and possible modifications of the surface quantum critical point near x(c)similar to 0.5.