Inversion Symmetry and Wave-Function Nodal Lines of Dirac Electrons in Organic Conductor α-( BEDT-TTF)2I3

By examining the organic conductor alpha-(BEDT-TTF)(2)I-3, which is described by a nearest neighbor tight-binding model, it is shown that, owing to inversion symmetry, each component of a wave function (WF) exhibits nodal lines (NLs) (i.e., lines in the two-dimensional Brillouin zone where the WF component vanishes). In the absence of any band crossing, each NL connects two time reversal invariant momenta (TRIMs) as partners. In the presence of a pair of Dirac points (band crossing), there are NLs that connect the pair of Dirac points via a TRIM without a partner. This second kind of NL leads to a discontinuous sign change for nonvanishing components of the WF. Such a property is the origin of the perpendicular to pi Berry phase accumulated on a contour integral encircling one Dirac point. The results are exemplified by the numerical calculation of WF components for the above conductor with a 3/4 filled band.