Thermoelectric transport of type-I, II, and III massless Dirac fermions in two-dimensional lattice model

TL;DR

This paper investigates the transport properties of massless Dirac fermions across different cone types in a 2D lattice, revealing unique behaviors at the critical type-III point and optimal tilting conditions.

Contribution

It introduces a lattice model that allows continuous tuning between type-I, II, and III Dirac cones, analyzing their distinct thermoelectric transport characteristics.

Findings

Type-III Dirac fermions exhibit unique transport behaviors distinct from types I and II.

Maximum thermoelectric response occurs at an optimally tilted type-I Dirac cone.

The figure of merit reaches 0.18 at optimal tilting, indicating potential for thermoelectric applications.

Abstract

We study longitudinal electric and thermoelectric transport coefficients of Dirac fermions on a simple lattice model where tuning of a single parameter enables us to change the type of Dirac cones from type-I to type-II. We pay particular attention to the behavior of the critical situation, i.e., the type-III Dirac cone. We find that the transport coefficients of the type-III Dirac fermions behave as the limiting case of neither the type-I nor type-II. On the one hand, the qualitative behaviors of the type-III case are similar to those of the type-I case. On the other hand, the transport coefficients do not change monotonically upon increasing the tilting; namely, the largest thermoelectric response is obtained not for the type-III case but for the optimally tilted type-I case. For the optimal case, the sizable transport coefficients are obtained; for example, the dimensionless figure of merit is 0.18.