Growth Dynamics of Photoinduced Domains in Two-Dimensional Charge-Ordered Conductors Depending on Stabilization Mechanisms

Abstract

Photoinduced melting of horizontal-stripe charge orders in\nquasi-two-dimensional organic conductors\n\\theta-(BEDT-TTF)2RbZn(SCN)4[BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene]\nand\n \\alpha-(BEDT-TTF)2I3 is investigated theoretically. By numerically solving\nthe time-dependent Schr\\"odinger equation, we study the photoinduced dynamics\nin extended Peierls-Hubbard models on anisotropic triangular lattices within\nthe\n Hartree-Fock approximation. The melting of the charge order needs more energy\nfor \\theta-(BEDT-TTF)2RbZn(SCN)4 than for \\alpha-(BEDT-TTF)2I3, which is a\nconsequence of the larger stabilization energy in \\theta-(BEDT-TTF)2RbZn(SCN)4.\nAfter local photoexcitation in the charge ordered states, the growth of a\nphotoinduced domain shows anisotropy. In \\theta-(BEDT-TTF)2RbZn(SCN)4, the\ndomain hardly expands to the direction perpendicular to the horizontal-stripes.\nThis is because all the molecules on the hole-rich stripe are rotated in one\ndirection and those on the hole-poor stripe in the other direction. They\nmodulate horizontally connected transfer integrals homogeneously, stabilizing\nthe charge order stripe by stripe. In \\alpha-(BEDT-TTF)2I3, lattice distortions\nlocally stabilize the charge order so that it is easily weakened by local\nphotoexcitation. The photoinduced domain indeed expands in the plane. These\nresults are consistent with recent observation by femtosecond reflection\nspectroscopy.\n