Quantum and Spontaneous Breakage of Translational Symmetry due to Light Excitation in Photo-Induced Structural Phase Transitions

K. Nasu Institute of Material Structure Science, KEK, 1-1, Oho, Tsukuba, 305-0801, Japan

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Real time quantum dynamics of the spontaneous translational symmetry breakage due to light excitation in the early stage of photo-induced structural phase transitions is reviewed under the guide of the Toyozawa theory, which is in exact compliance with the conservation law of the total momentum. At the Franck-Condon state, an electronic excitation just created by a visible photon is in a plane wave state, extended all over the crystal. While, after the lattice relaxation having been completed, it is localized as a new excitation. So, is there the shrinkage of the excitation wave function? No! The wave function never shrinks, but only the spatial (or inter lattice-site) quantum coherence (interference) of the excitation disappears, as the lattice relaxation proceeds. This is the breakage of translational symmetry.

DOI: 10.12693/APhysPolA.121.347 PACS numbers: 78.90.+t