Abstract
Dirac electrons with a zero-gap state (ZGS) in organic conductor α-(BEDT- TTF)2I3 result from a fine tuning of the seven nearest neighbors transfer integrals (a1,a2,a3,b1,b2,b3,b4) between the four molecules of the unit cell. In this work we show that for given moduli |a11,...|b41, the possibility of having Dirac electron with a ZGS at 3/4 (or 1/4) filling strongly depends on the specific configurations of signs of the seven transfer integral. More precisely it is possible to classify the sign configurations into essentially four classes determined by χa = sign(a2a3) and χb = sign(b1b2b3b4). Using extended numerics, we show that for both weak and large inhomogeneity in the moduli, the class (χa,χb) = (—, —) is the most favorable to find Dirac electrons with ZGS at 3/4 (or 1/4) filling. For the class (χa,χb) = (+, +) in the opposite case, we never found any ZGS at either 1/4 or 3/4 filling. The last two classes given by (χa,χb) = (+, —) and (χa,χb) = (—, +) corresponding to an intermediate situation; they allow for ZGS at 3/4 (resp. 1/4) filling but are much less favorable than class (χa, χb) = (—, —). As a matter of fact, all previous numerical studies of Dirac electrons and ZGS in α-(BEDT-TTF)2I3 correspond to class (χa,χb) = (—, +).
Highlights
It is well established that organic conductors α-(BEDT-TTF)2I3 [1], exhibit a zero gapstate (ZGS) characteristic of the presence of massless Dirac electrons close to the Fermi energy [2]
Summary In summary, we have examined the existence of ZGS at 3/4 filling for a tight binding model with seven nearest neighbors transfer integrals (a1, a2, a3, b1, b2, b3, b4) between the four molecules of the unit cell, as in α-type organic conductor
We have systematically studied the combined role of the sign and moduli of the transfer integrals on the appearance of ZGS at 3/4 filling
Summary
It is well established that organic conductors α-(BEDT-TTF)2I3 [1], exhibit a zero gapstate (ZGS) characteristic of the presence of massless Dirac electrons close to the Fermi energy [2]. The purpose of the present work is to clarify the relative role played by the the inhomogeneity in the moduli and in the signs of the seven transfer integrals on the appearance and stability of Dirac electrons with ZGS. As explained in more details below, for given moduli |a1|, ...|b4|, the possibility of having Dirac electron with a ZGS at 3/4 (or 1/4) filling strongly depends on the specific configurations of signs of the seven transfer integral. 3. Classification in terms of chirality patterns For fixed moduli (|a1|, · · · |b4|), the energy bands En(k) and the eigenfunction components ujn(k) have the freedom of the sign of the seven hopping parameters, as a result one may expected to obtain 27 distinct LDOS Dj(E). Without loss of generality, it is always possible to fix arbitrarily the sign of three out of the seven transfer integrals and hereafter the convention (b1, b2, b3) > 0 is adopted in all numerical computations
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