First-Principles Study of Electronic Structure in α-(BEDT-TTF)₂I₃at Ambient Pressure and with Uniaxial Strain

Abstract

Within the framework of the density functional theory, we calculate the electronic structure of α-(BEDT-TTF)2I3 at 8 K and room temperature at ambient pressure and with uniaxial strain along the a-and b-axes. We confirm the existence of anisotropic Dirac cone dispersion near the chemical potential. We also extract the orthogonal tight-binding parameters to analyze physical properties. An investigation of the electronic structure near the chemical potential clarifies that effects of uniaxial strain along the a-axis is different from that along the b-axis. The carrier densities show T 2 dependence at low temperatures, which may explain the experimental findings not only qualitatively but also quantitatively.

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

“…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 .…”

“…It is the ZGS where the chemical potential coincides with the contact points of two cones facing each other. The existence of the ZGS is verified by first-principles calculations [32,33], which suggest the ZGS at ambient pressure. The tilted Weyl equation is proposed as the effective Hamiltonian describing the motion of electrons and holes in the vicinity of the contact point [34].…”

“…We note that the contact points exist but the chemical potential slightly leaves the contact points. The first-principles calculation also indicates that the electronic system at ambient pressure has the contact points, although the chemical potential leaves the contact points with increasing T [33]. The charge disproportionation is essentially due to the inequivalency of the BEDT-TTF sites in a unit cell.…”

“…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…”

“…To study the anomalous temperature dependences of the Hall coefficient, the Hall and electric conductivities are investigated theoretically for the massless Dirac electrons described using the tilted Weyl equation. The strong enhancement of the Hall coefficient toward low temperatures is shown [55] by taking the interband effects of magnetic field exactly into account in the Luttinger-Kohn representation and using the expected temperature dependence of the chemical potential [33]. The sharp but continuous reversal of the sign of the Hall coefficient is possible if the extremely small amount of electron doping, approximately 1 ppm, exists.…”