Electronic properties close to Dirac cone in two-dimensional organic conductor α-(BEDT-TTF)2I3

Abstract

Abstract. A zero-gap state (ZGS) has been found in a bulk system of two-dimensional organic conductor, α-(BEDT-TTF)2I3 salt which consists of four sites of donor molecules in a unit cell. In the present paper, the characteristic of the ZGS is analyzed in detail and the electronic properties are examined in the vicinity of the Dirac point where the conduction and valence bands degenerate to form the zero-gap. The eigenvectors of the energy band have four components of respective sites, where two of them correspond to inequivalent sites and the other two correspond to equivalent sites. It is shown that the former exhibits an exotic momentum dependence around the contact point and the latter shows almost a constant dependence. The density of states of each site close to the Dirac point is calculated to demonstrate the temperature dependence of the local magnetic susceptibility and the local nuclear magnetic relaxation rate. Further, the robust property of the ZGS against the anion potential is also shown by using the second-order perturbation.PACS. 71.10.-w Theories and models of many-electron systems -72.80.Le Polymers; organic compounds (including organic semiconductors)

Theoretical study of the zero-gap organic conductor α-(BEDT-TTF)2I3

“…Then the charge disproportionation does not break any symmetry of crystal and does not have any phase transition. Recent theoretical results on the charge disproportionation [15] are consistent with the x-ray experiment [16] and NMR experiment [17]. The charge disproportionation exists in the ZGS theoretically [34].…”

“…The charge orderings appearing in both those two phases are the horizontal stripe, and do not exhibit any phase transitions between them. Recent theoretical estimation on charge on each site [15], based on the transfer energies obtained by the first-principles calculation [33], is consistent with both the x-ray experiment [16] and the NMR experiment [12], where the A and B sites are hole-rich and the A and C sites are electron-rich. The ZGS emerges with a further increase of P a .…”

“…The Raman studies suggest the charge ordering in the insulating phase below T MI and also charge disproportionation above T MI [13,14]. Recent theoretical results on the charge disproportionation [15] are consistent with the x-ray experiment and NMR experiment [16,17].…”

“…Figure 5 [15,57] shows the DOS, ρ α (ω), on each BEDT-TTF site α = A, A , B, C in a unit cell, calculated using the data obtained by Kino and Miyazaki [33], where…”

“…This indicates that the site C mainly contributes to the ZGS. The inclinations of ρ α (ω) affect the properties induced by low-energy excitations, such as the Knight shift K and the 1/T 1 of the NMR experiments [15,58,59]. , where the vertical axis represents the band energy in eV, on the k x -k y plane in radian [57].…”