The resistance between two arbitrary grid points of several infinite lattice structures of resistors is calculated by using lattice Green’s functions. The resistance for d dimensional hypercubic, rectangular, triangular, and honeycomb lattices of resistors is discussed in detail. Recurrence formulas for the resistance between arbitrary lattice points of the square lattice are given. For large separation between nodes the asymptotic form of the resistance for a square lattice and the finite limiting value of the resistance for a simple cubic lattice are calculated. The relation between the resistance of the lattice and the van Hove singularity of the tight-binding Hamiltonian is given. The Green’s function method used in this paper can be applied in a straightforward manner to other types of lattice structures and can be useful didactically for introducing many concepts used in condensed matter physics.

We present a unified treatment of Zitterbewegung phenomena for a wide class of systems including spintronic, graphene, and superconducting systems. We derive an explicit expression for the time dependence of the position operator of the quasiparticles which can be decomposed into a mean part and an oscillatory term. The latter corresponds to the Zitterbewegung. To apply our result for different systems, one needs to use only vector algebra instead of the more complicated operator algebra.

We study the dynamics of the electrons in a nonuniform magnetic field applied perpendicular to a graphene sheet in the low-energy limit when the excitation states can be described by a Dirac-type Hamiltonian. Compared to two-dimensional electron gas systems, we show that snake states in graphene exhibit peculiar properties related to the underlying dynamics of the Dirac fermions. The current carried by snake states is locally uncompensated, leading to a current inhomogeneity in the ground state.

We show that the wave functions form caustics in circular graphene $p\mathrm{\text{−}}n$ junctions which in the framework of geometrical optics can be interpreted with a negative refractive index.

Using a reformulated Kubo formula we calculate the zero-energy minimal conductivity of bilayer graphene taking into account the small but finite trigonal warping. We find that the conductivity is independent of the strength of the trigonal warping and it is 3 times as large as that without trigonal warping and 6 times larger than that in single layer graphene. Although the trigonal warping of the dispersion relation around the valleys in the Brillouin zone is effective only for low-energy excitations, our result shows that its role cannot be neglected in the zero-energy minimal conductivity.

We calculated the minimal longitudinal conductivity in prefect single and bilayer graphene by extending the two methods developed for Dirac fermion gas by A. W. W. Ludwig et al. in Phys. Rev. B {\bf 50}, 7526 (1994). Using the Kubo formula which was originally applied for spintronic systems we obtain $\sigma^{\text min}_{xx}= (J \pi /2) e^2/h$ while from the other formula used in the above mentioned work we find $\bar{\sigma}^{\text min}_{xx}= (4J/\pi) e^2/h$, where J=1 for single layer and J=2 for bilayer graphene. The two universal values are different although they are numerically close to each other. Our two results are in the same order of magnitude as that of experiments and for single layer case one of our result agrees many earlier theoretical predictions. However, for bilayer graphene only two studies are known with predictions for the minimal conductivity different from our calculated values. Similarly to the single layer case, the physical origin of the minimal conductivity in bilayer graphene is also rooted back to the intrinsic disorder induced by the Zitterbewegung which is related to the trembling motion of the electron.Comment: 4 pages, no figure, corrected typos and added references in v