Charge Distribution in the Surface BEDT-TTF Layer of α-(BEDT-TTF)₂I₃at Room Temperature with Scanning Tunneling Microscopy

Wavefunction Analysis of STM Image: Surface Reconstruction of Organic Charge Transfer Salts

“…The charge distribution in the surface (ET) 2 layer is analyzed with the wavefunction analysis described in the previous section [1]. Figures 8 and 9 show the observed STM images in the ab plane, where the higher the probe tip, the brighter the topography appears.…”

“…The parentheses show uncertainty in the last digit (reused from Ref. [1]). Figure 9B shows the STM image with the structure determined by X-ray analysis [23], where the position and direction of the bright areas agree with the 3p orbitals of the sulfur atoms without recognizable reconstructions.…”

“…However, since STM images are constructed with the electron tunneling probability between the wavefunctions of an STM probe tip and those of a sample surface, it is required for us to analyze the wavefunctions of the atoms and the molecules in the surface layer to extract structural information. In this chapter, some examples of the wavefunction analysis [1] are demonstrated in the organic charge transfer salts composed of electron donor and electron acceptor molecules, in which the van der Waals interaction and the π electron transfer integrals between like molecules, and the Coulomb attractive interaction between unlike molecules govern the formation of the crystals. Since the van der Waals interaction between the like molecules is relatively weak, the analysis of atomic π orbitals of sulfur, oxygen, and carbon atoms of the donor molecules would be a good approximation for the wavefunction analysis of STM images.…”

“…Thus, we are possible to continuously control the structure of the π electron networks from 1D to 2D, the filling of the π electron bands and electron-electron correlation of π bands, resulting in not only non-BCS superconductor, but also metals with variety of ground states like antiferromagnetic (AF), charge density wave (CDW), spin density wave (SDW), spin Peierls (SP), charge ordering (CO) states, and their combinations with exotic magnetic structures, for example, magnetic-field induced superconductivity [7]. Then, STM investigation of these organic systems is useful to collect local information of the π electron systems of the crystal surface layer [1,[8][9][10][11][12][13][14][15][16][17][18].…”

“…On the second point, the partner anion layer of the double layer generally forms a flat sheet and generates approximately uniform electric field normal to the anion layer [1]. The uniform electric field attracts uniformly the cation layer sheet, in which the cation molecules are tightly bound each other by the cohesive interaction with the other cation molecules, forming a π band, under constraint of the steric hindrance with the cation molecules and the partner anion molecules in the double layer.…”