Controllable Nernst and Seebeck effects in graphene with O-shaped Kekulé structure

The Nernst and Seebeck effects in graphene with uniform Kekulé lattice distortion have been studied using the tight-binding model combined with the nonequilibrium Green's function method. Numerical results of this work showed that due to the electron–hole symmetry, the Nernst coefficient is an even function of the Fermi energy, while the Seebeck coefficient is an odd function regardless of the magnetic field. The Nernst and Seebeck coefficients show peaks when the Fermi energy crosses the Landau levels at high magnetic fields or crosses the transverse subbands at the zero magnetic fields. The peak height can be very large when the Fermi energy approaches the Dirac point, the Seebeck coefficient can reach about 0.78 mV/K, and the Nernst coefficient can reach about 0.95 mV/K at the corresponding hopping energy modification parameter $δ = 0.03$ and $T = 0.009 t / k B ≈ 288$ K. When $δ = 0.08$ and $T = 0.024 t / k B ≈ 766$ K, the Seebeck coefficient (or Nernst coefficient) is still up to about 0.78 mV/K (or 0.95 mV/K). This suggests that tunable Seebeck and Nernst coefficients can be achieved because the bandgap is a function of the corresponding hopping energy modification parameter $δ$⁠. Experimentally, $δ$ can be modulated by changing the type and amount of atoms adsorbed on graphene. In strong magnetic fields, the Nernst coefficient does not depend on the chirality of the nanoribbon.