Oleg Berman

By Oleg L. Berman, Vladimir S. Boyko, Roman Ya. Kezerashvili and Yurii E. Lozovik

Part of the book: Wave Propagation

By Sita Kandel, Godfrey Gumbs and Oleg L. Berman

We present a semi-analytical expression for both longitudinal and transverse optical conductivities of a model TNLSM employing the Kubo formula with emphasis on the optical spectral weight redistribution, deduced from appropriate Green’s functions. In this semimetal, the conduction and valence bands cross each other along a one- dimensional curve protected by certain symmetry group in the 3D Brillouin zone. Although the crossing cannot be removed by any perturbations, it can be adjusted by continuous tuning of the Hamiltonian with a parameter α. When α>0, the two bands cross each other near the Γ point in the (kx,ky) plane of the first Brillouin zone making a nodal circle of radius α. The circle shrinks to point when α=0 and for α<0, the nodal circle vanishes and a gap opens around Γ. Numerical results for the longitudinal optical response of such TNLSM are investigated by varying the gap due to modifying α, the chemical potential μ, temperature T and the dephasing parameter η. The longitudinal optical conductivity is anisotropic along the direction parallel or perpendicular to the nodal ring. However, the transverse optical conductivity vanishes due to rotational symmetry.

Part of the book: Advances in Nanosheets