Collective Excitations in the Charge-Ordered Phase of α-(BEDT-TTF)2I3

The charge response of a charge-ordered state in the organic conductor alpha-(BEDT-TTF)(2)I-3 is characterized by dc resistivity, dielectric and optical spectroscopy in different crystallographic directions within the two-dimensional conduction layer. Two dielectric modes are detected. The large mode is related to the phasonlike excitation of the 2k(F) bond-charge density wave which forms in the ab plane. The small dielectric mode is associated with the motion of domain-wall pairs along the a and b axes between two types of domains which are created due to inversion symmetry breaking.