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Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids

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Published on: May 27, 2020

Short-Range Excitonic Phenomena in Low-Density Metals.

Jaakko Koskelo^1,2, Lucia Reining^1,2, Matteo Gatti^1,2,3

¹Institut Polytechnique de Paris, LSI, CNRS, CEA/DRF/IRAMIS, École Polytechnique, F-91120 Palaiseau, France.

Physical Review Letters

|February 14, 2025

Summary

Excitonic effects, typically weak in metals, emerge in low-density electron gases due to reduced screening. These findings reveal novel low-energy collective modes with excitonic properties.

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Area of Science:

Condensed matter physics
Quantum mechanics

Background:

Excitonic effects are generally considered weak in metals due to strong Coulomb screening.
Recent theoretical suggestions point to the possibility of low-energy excitonic collective modes in the homogeneous electron gas.

Purpose of the Study:

To investigate the existence and nature of low-energy excitonic collective modes in the low-density homogeneous electron gas.
To explore the role of reduced screening and electron-hole correlations in these phenomena.

Main Methods:

Utilizing the Bethe-Salpeter equation (BSE) for ab initio calculations.
Addressing and overcoming the self-polarization error in standard BSE approximations.
Analyzing the electron-hole wave function to determine excitonic character.

Main Results:

Confirmed the emergence of low-energy collective modes in the low-density electron gas.
Demonstrated that reduced screening at short distances facilitates these excitonic effects.
Observed strong, anisotropic electron-hole correlations characteristic of excitonic behavior.
Showcased the capability of the adiabatic local density approximation to capture these effects.

Conclusions:

Low-density electron gases can exhibit significant excitonic effects, challenging conventional understanding.
These findings highlight the importance of short-distance electron-hole interactions and reduced screening.
The identified exotic regime may be observable in doped semiconductors and interfaces.