Oscillations in the radiative damping of plasma resonances in a gated disk of 2D electron gas

TL;DR

This paper investigates how the presence of a metal gate influences the radiative damping and resonance line widths of plasma oscillations in a 2D electron gas disk, revealing oscillatory behavior due to electromagnetic interference.

Contribution

It provides a combined numerical and analytical analysis of plasma resonance line widths considering both collisional and radiative losses, highlighting the impact of gate proximity on damping mechanisms.

Findings

Radiative broadening can dominate in high mobility samples.

Proximity to the gate reduces the line width, approaching purely collisional broadening.

Oscillations in line width occur as the disk moves away from the gate, due to interference effects.

Abstract

We calculate the absorption spectra of a conductive disk in the presence of a metal gate. In our analysis, we use the conductivity described by the Drude model. We examine the frequency and line width of the absorption resonances associated with the excited plasma waves. They are estimated both numerically and analytically for the fundamental and axisymmetric plasma modes. The line width is determined by the collisional and radiative losses. In high mobility samples, the latter may dominate even when the resonant frequencies can be described by a standard quasistatic approximation, i.e., neglecting electromagnetic retardation. Placing a metal near the disk drastically affects the radiative broadening of the line width due to the interference of electromagnetic fields created by the disk and the metal charges. Bringing the disk in close proximity to the gate makes the total field almost vanish. In that case, the line width is defined solely by the collisional broadening. As the disk is moved away from the gate, the line width first shows a reduction since the plasmon transforms into plasmon-polariton, which is dressed with undamped electromagnetic field surrounding the disk. Then it increases and exhibits decaying oscillations, reaching the asymptotic value of the ungated disk.