# Regensburg 2016 – wissenschaftliches Programm

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# HL: Fachverband Halbleiterphysik

## HL 36: Poster Ib

### HL 36.21: Poster

### Dienstag, 8. März 2016, 15:00–19:00, Poster A

**Microscopic Theory of the Refractive Index** — •Ronald Starke^{1} and Giulio Schober^{2} — ^{1}TU Bergakademie Freiberg, Inst. f. theo. Phys — ^{2}Uni. Heidelberg, Inst. f. theo. Phys

We re-examine the refractive index from the viewpoint of modern first-principles materials physics and find that the standard formula, *n*^{2} = є_{r} µ_{r}, is downright wrong. Even worse, the allegedly approximate Maxwell relation,
*n*^{2} = є_{r}, which is being used for most practical purposes, can only be justified in the long-wavelength limit. In order to obtain the true wave-equation in materials, one instead has to start from the fundamental, Lorentz covariant electromagnetic wave-equation in terms
of the proper response tensor. From this we prove a general theorem by which the electric field in materials is restricted to the kernel of the microscopic dielectric tensor thus elucidating the analogy to the theory of plasmons.