Europhys. Lett.
Volume 72, Number 6, December 2005
Page(s) 1018 - 1024
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 04 November 2005
Europhys. Lett., 72 (6), pp. 1018-1024 (2005)
DOI: 10.1209/epl/i2005-10321-x

Anomalous optical absorption in a random system with scale-free disorder

E. Díaz1, A. Rodríguez2, F. Domínguez-Adame1 and V. A. Malyshev3

1  GISC, Departamento de Física de Materiales, Universidad Complutense E-28040 Madrid, Spain
2  GISC, Departamento de Matemática Aplicada y Estadística, Universidad Politécnica E-28040 Madrid, Spain
3  Institute for Theoretical Physics and Materials Science Centre University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands

received 18 July 2005; accepted in final form 13 October 2005
published online 4 November 2005

Optical spectroscopy usually fails in detecting localization-delocalization (Anderson) transitions. We report on an anomalous behavior of the absorption spectrum in a one-dimensional lattice with long-range correlated diagonal disorder, having a power-like spectrum $S(k) \sim 1/k^{\alpha}$. This type of correlations gives rise to a phase of extended states at the band center, provided $\alpha$ is larger than a critical value $\alpha_c$. We show that for $\alpha < \alpha_c$, the absorption spectrum is single-peaked, while an additional peak arises when $\alpha > \alpha_c$, signaling the occurrence of the Anderson transition. The peak is located slightly below the low-energy mobility edge, providing a unique spectroscopic tool to monitor the latter. We present qualitative arguments explaining this anomaly.

78.30.Ly - Disordered solids.
71.30.+h - Metal-insulator transitions and other electronic transitions.
71.35.Aa - Frenkel excitons and self-trapped excitons.

© EDP Sciences 2005