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1230-MM04-08

Terahertz-induced Kerr-effect in Relaxor Ferroelectrics Matthias C. Hoffmann1,2, Harold Y Hwang2, Nathaniel C. Brandt2, Ka-Lo Yeh2 and Keith A. Nelson2 1 Max Planck Group for Structural Dynamics, University of Hamburg, CFEL, Hamburg, Germany 2 Massachusetts Institute of Technology, 77 Massachusetts Ave, Cambridge, MA, 02139, USA ABSTRACT We demonstrate the Kerr-effect induced by the electric field of single-cycle THz pulses in the relaxor ferroelectrics potassium tantalate/niobate KTa1-xNbxO3 (KTN) and K1-yLiyTa1-xNbxO3 (KLTN). We find a slow signal decay component with a time constant of 6 ps in KTN with x=1.8% at room temperature, that decreases upon approaching the transition temperature. INTRODUCTION Ferroelectrics, by definition, have spontaneous macroscopic electric polarizations that can be reversed by an applied electric field. At the Curie temperature Tc, the polar ferroelectrics undergo a phase transition to the nonpolar paraelectric phase. The collective reaction coordinate for this phase transition is the soft optic phonon mode, which oscillates in the terahertz (THz) frequency range. Normal ferroelectrics have macroscopic (long range) ferroelectric domains whereas relaxors may enter ferroelectric phases with true long-range order or dipole glass states with localized nanopolar domains [1, 2], depending on the dopant concentration of the impurity introduced. Above Tc, no polar domain exists in normal ferroelectrics but polar nanodomains persist well above the dynamic transition temperature of relaxors. Doping gives rise to dipolar defects, which transform the material into a relaxor. These impurities distort the highly polarizable host lattice, forming correlated polarization regions in the host lattice. At high impurity levels, the correlated regions overlap and the relaxor can enter into a long-range ordered ferroelectric state. It is also possible to form a dipole glass if the nanodomain orientations are frozen into place before they begin to interact as the temperature is reduced and their correlation lengths increase [3]. Near Tc the dielectric function ε’ can reach extremely high values, on the order of up to 105 at DC and in the microwave frequency range. Closely related to this are the extremely high electrooptic effects which are among the highest in known materials [4] and hence of great interest for technological applications [5]. In the cubic phase above Tc, KTN has inversion symmetry and the lowest order EO effect is the Kerr effect [6]. In the other phases, KTN is ferroelectric and the Pockels effect is observed since it does not have inversion symmetry [7]. Like the dielectric function, the electro-optic coefficient is known to have a strong frequency dependence [6], dropping sharply as GHz range frequencies are approached. Of interest are the optical and nonlinear optical behavior at higher frequencies when the TO soft phonon mode frequency is approached. The nonlinear dynamics of the relaxors at THz frequencies have not yet been extensively studied.. Here we demonstrate the