# Gate-Tunable Single Terahertz Meta-Atom Ultrastrong Light-Matter Coupling

## TL;DR

This paper demonstrates electrical tuning of ultrastrong light-matter interactions using a terahertz resonator and a two-dimensional electron gas.

## Contribution

The first demonstration of electrically tunable terahertz far-field spectroscopy in a GaAs quantum well heterostructure.

## Key findings

- Landau polariton dispersion is tunable via electric gate bias.
- Electron confinement down to 410 nm enables standing plasma wave excitation.
- Normalized coupling strength is tunable from η = 0.46 to η = 0.18.

## Abstract

We study the electrical tunability of ultrastrong light-matter
interactions between a single terahertz circuit-based complementary
split ring resonator (cSRR) and a two-dimensional electron gas. For
this purpose, transmission spectroscopy measurements are performed
under the influence of a strong magnetic field at different set points
for the electric gate bias. The resulting Landau polariton dispersion
depends on the applied electric bias, as the gating technique confines
the electrons in-plane down to extremely subwavelength dimensions
as small as d = 410 nm. This confinement allows for
the excitation of standing plasma waves at zero magnetic field and
an effective tunability of the electron number coupled to the THz
resonator. This allows the normalized coupling strength to be tuned
in situ from η = 0.46 down to η = 0.18. This is the first
demonstration of terahertz far-field spectroscopy of an electrically
tunable interaction between a single terahertz resonator and electrons
in a GaAs quantum well heterostructure.