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When going to the limits of temporal and spatial resolution strongly correlated systems reveal fascinating phases and phase transitions that root in the intricate interplay of spins, orbitals, electrons, and lattice. Here these phenomena are investigated by nonlinear spectroscopy with 100 fs lasers pulses. Regarding the temporal limit, I will show that on the ultrafast time scale the magnetization dynamics of antiferromagnetic compounds differs noticeably from that of ferromagnetic compounds. First, comparison of the dynamical properties of the model antiferromagnet Cr2O3 to model ferro- and ferrimagnets reveals that spin-lattice thermalization in an antiferromagnet is more complex and inherently faster than in compounds displaying a spontaneous magnetization. Second, ultrafast fully controlled and reversible three-dimensional switching is demonstrated for the antiferromagnetic order parameter of the exchange-bias compound NiO. Regarding the spatial limit, I will show that the two-dimensional conducting state formed at the interface between the perovskite compounds LaAlO3 and SrTiO3 (S. Thiel et al.: Science 313, 1942 (2006)) can be conveniently probed by interface sensitive nonlinear optics. |
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