Electrical and thermoelectrical transport in Dirac fermions through a quantum dot

TL;DR

This paper studies how massless Dirac fermions conduct electricity and generate thermoelectric effects through a quantum dot, revealing unique behaviors at the Dirac point and near a quantum impurity transition.

Contribution

It introduces a detailed analysis of thermoelectric transport in Dirac fermions using a pseudogap Anderson model, highlighting novel conductance and thermopower phenomena.

Findings

Conductance has a cusp at the Dirac point with sign-changing thermopower.

A quantum impurity transition affects the Kondo temperature and conductance peak.

Thermopower magnitude exceeds $k_B/e$, and thermoelectric efficiency surpasses unity.

Abstract

We investigate the conductance and thermopower of massless Dirac fermions through a quantum dot using a pseudogap Anderson model in the non-crossing 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 illustrates 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 $k_B/e$, and the thermoelectric figure of merit exceeds unity.