We show that the low-frequency absorbance of undoped graphene, silicene, and germanene has a universal value, only determined by the Sommerfeld fine-structure constant. This result is derived by means of ab initio calculations of the complex dielectric function for optical interband transitions applied to two-dimensional (2D) crystals with honeycomb geometry. The assumption of chiral massless Dirac fermions is not necessary. The low-frequency absorbance does not depend on the group-IV atom, neither on the sheet buckling nor on the orbital hybridization. We explain these findings via an analytical derivation of the relationship between absorbance and fine-structure constant for 2D Bloch electrons. The effect of deviations of the electronic bands from linearity is also discussed. DOI: 10.1103/PhysRevB.87.035438
Matthes, L., Gori, P., Pulci, O., Bechstedt, F. (2013). Universal infrared absorbance of two-dimensional honeycomb group-IV crystals. PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS, 87(3) [10.1103/PhysRevB.87.035438].
Universal infrared absorbance of two-dimensional honeycomb group-IV crystals
PULCI, OLIVIA;
2013-01-01
Abstract
We show that the low-frequency absorbance of undoped graphene, silicene, and germanene has a universal value, only determined by the Sommerfeld fine-structure constant. This result is derived by means of ab initio calculations of the complex dielectric function for optical interband transitions applied to two-dimensional (2D) crystals with honeycomb geometry. The assumption of chiral massless Dirac fermions is not necessary. The low-frequency absorbance does not depend on the group-IV atom, neither on the sheet buckling nor on the orbital hybridization. We explain these findings via an analytical derivation of the relationship between absorbance and fine-structure constant for 2D Bloch electrons. The effect of deviations of the electronic bands from linearity is also discussed. DOI: 10.1103/PhysRevB.87.035438I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.