Effect of Tilting on the In-Plane Conductivity of Dirac Electrons in Organic Conductor

We examine the in-plane electric conductivity of Dirac electrons with a tilted cone in terms of the degree of the tilting eta and the angle alpha measured from the applied electric field. It is demonstrated that a noticeable difference in the conductivity exists between alpha = 0 and pi/2, which corresponds to the tilting being parallel and perpendicular to the field, respectively. With increasing tilting parameter eta (0 <= eta < 1), the conductivity in the parallel case increases but remains finite, while that in the perpendicular case increases and diverges for eta -> 1. The effect of doping is also examined by varying the chemical potential. We further show the conductivity for the arbitrary angle alpha, which induces an additional current perpendicular to the electric field with the deviation angle phi. Such an anisotropic conductivity gives phi < 0 for 0 < alpha < pi/2 and phi > 0 for pi/2 < alpha < pi. We propose an experiment to determine alpha and eta.