STM study on the charge order phase of theta-(BEDT-TTF)(2)RbZn(SCN)(4)

摘要

The organic conductor theta-(BEDT-TTF)(2)RbZn(SCN)(4), which exhibits charge ordering below T-CO = 190 K was studied by STM to observe the charge ordering pattern in the real space. The conducting a-c plane was investigated. The donor arrangement in the a-c surface was clearly observed in topographic STM images at room temperature. The STM image shows the rectangular pattern with periods of 1 nm and 0.5 nm along the a- and c-direction, respectively. This means that BEDT-TTF donors located at the center of the rectangle were not observed except a certain scan. The observed STM image is naively expected from the crystal structure of theta-(BEDT-TTF)(2)RbZn(SCN)(4). We found that all donors can be imaged by the scan along the a-axis. The STM image at 170 K shows the nearly two-fold periodicity along the c-direction. It corresponds to the horizontal stripe charge order pattern.