Applying the resonant-state expansion to realistic materials with frequency dispersion

Sehmi, H. S., Langbein, W. ORCID: https://orcid.org/0000-0001-9786-1023 and Muljarov, E. A. ORCID: https://orcid.org/0000-0002-2878-4148 2020. Applying the resonant-state expansion to realistic materials with frequency dispersion. Physical Review B 101 (4) , 045304. 10.1103/PhysRevB.101.045304

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Abstract

The dispersive resonant-state expansion, developed for an accurate calculation of the resonant states in open optical systems with frequency dispersion, is applied here to realistic materials, such as metallic nanoparticles and semiconductor microspheres. The material permittivity is determined by fitting the measured indices of refraction and absorption with a generalized Drude-Lorentz model containing a number of poles in the complex frequency plane. Each Drude or Lorentz pole generates an infinite series of resonant states. Furthermore, for small nanoparticles, each of these poles produces a distinct surface plasmon polariton mode. The evolution of these multiple surface modes with increasing radius traces the transition from the electrostatic limit to significant retardation and radiation. Treating the optical phonon range in a semiconductor microsphere, a reststrahlen band separating the resonant states is found. Considering a small energy range around the semiconductor band gap, the transition from absorption to gain is described by inverting the Lorentz pole weight, which results in the formation of lasing resonant states. Interestingly, the series of resonant states converging towards the absorption pole from the lower frequency side reshapes for a gain pole into a clockwise loop approaching the pole from the higher frequency side, being separated from a series spanning from low to high frequencies and containing the lasing modes.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Physical Society
ISSN:	2469-9950
Date of First Compliant Deposit:	27 January 2020
Date of Acceptance:	23 January 2020
Last Modified:	02 May 2023 12:32
URI:	https://orca.cardiff.ac.uk/id/eprint/129068

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