Topological Domain Wall and Valley Hall Effect in Charge Ordered Phase of Molecular Dirac Fermion System α-(BEDT-TTF)2I3

The topological domain wall and valley Hall effect are theoretically investigated in the molecular conductor alpha-(BEDT-TTF)(2)I-3. By using the mean-field theory in an extended Hubbard model, it is demonstrated under a cylinder boundary condition that a domain wall emerges in the charge ordered phase, and exhibits a topological nature near the phase transition to the massless Dirac Fermion phase. The topological nature is well characterized by the Berry curvature, which has opposite signs in two charge ordered phases divided by the domain wall, and gives rise to the valley Hall conductivity with opposite signs, enabling these phases to be distinguished. It is also found that the valley Hall conductivity in the tilted Dirac cones exhibits a characteristic double-peak structure as a function of chemical potential using the semi classical formalism.