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Dynamics of phase transitions forms an important and rapidly growing area of condensed matter physics, which touches some other areas of science ranging from geology to modeling of traffic dynamics. This presentation addresses an importance of symmetry relations between adjoined phases that plays a crucial role in phase transition dynamics. In particular it is suggested that phase transitions involving an increase of the symmetry of the material may occur on a very fast time scale, whereas in the opposite case the phase transition is intrinsically slow. As a particular example we have tested the dynamics of spin, orbital and structural phase transitions in yttrium vanadate (YVO3) by means of optical pump-probe and time-resolved x-ray diffraction techniques. The experimental results demonstrate a rapid destruction of spin order within less than 4 ps after an optical excitation. In contrast, dynamics of structural transition associated with an increase in YVO3 lattice symmetry occurs on a nanosecond timescale in agreement with the proposed symmetry rule. |
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