Electrical and Thermoelectrical Transport Properties of Dirac Fermions through a Quantum Dot

We investigate the conductance and thermopower of massless Dirac fermions through a quantum dot using a pseudogap Anderson model in a noncrossing approximation. When the Fermi level is at the Dirac point, the conductance has a cusp where the thermopower changes its sign. When the Fermi level is away from the Dirac point, the Kondo temperature shows a quantum impurity transition between an asymmetric strong-coupling Kondo state and a localized moment state. The conductance shows a peak near this transition and reaches the unitary limit at low temperatures. The magnitude of the thermopower exceeds \(k_{\text{B}}/e\), and the thermoelectric figure of merit exceeds unity.