Difference between Photoinduced Phase and Thermally Excited Phase

概要

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We study differences between the photoinduced phase and the thermally excited one, using a two-dimensional Peierls-Hubbard model, which includes a strong electron-phonon coupling and an on-site interelectron repulsion, as well as an anharmonic lattice potential. Because of this anharmonicity, the system undergoes a first order phase transition from an insulating CDW state to a metallic one at a high temperatuere. Although some sign of an SDW order is expected to appear due to this repulsion, it is hidden in all these equilibrium phases. In fact, it is hidden, not only in the CDW ground state, but also in this metallic one, since the high temperature itself destroys the SDW order, far before the CDW-metal transition occurs. While, a photo-excitation at low enough temperature is shown to generate a locally metastable SDW domain. Therefore, to observe the presence of such a hidden interaction and its resultant broken symmetry, a nonquilibrium photoinduced phase is shown to be most straightforward. Thus, the photoinduce phase transition can make an interaction appear as a broken symmetry only in this phase, even though this interaction is almost completely hidden or killed in all the equilibrium phases from low temperature to high ones.
社団法人日本物理学会の論文
2002-04-15