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  Maerten, L.; Bojahr, A.; Gohlke, M.; Roessle, M.; Bargheer, M.: Coupling of GHz Phonons to Ferroelastic Domain Walls in SrTiO₃. Physical Review Letters 114 (2015), p. 047401/1-5

10.1103/PhysRevLett.114.047401

Abstract:
We study the linear and nonlinear acoustic response of SrTiO3 across its ferroelastic transition at Ta=105  K by time domain Brillouin scattering. Above Ta we observe that for a strain amplitude of ∼0.18% the sound velocity for compressive strain exceeds the tensile strain velocity by 3%. Below Ta we find a giant slowing down of the sound velocity by 12% and attribute this to the coupling of GHz phonons to ferroelastic twin domain walls. We propose a new mechanism for this coupling on the ultrafast time scale, providing an important new test ground for theories used to simulate atomic motion in domain forming crystals.