Observation of a near-surface structural phase transition in SrTiO3 by optical second harmonic generation.

A near-surface structural phase transition on a SrTiO3 single crystal, occurring at T(*) about 45 K above the bulk cubic-to-tetragonal transition, is observed by means of optical second harmonic generation. The temperature dependence of the second harmonic field in the vicinity of T(*) is described with a phenomenological Landau-type model.