Elsa Jöchl, Anna-Lydia Vieli, Lucy Hale, Felix Helmrich, Deniz Turan, Mona Jarrahi, Mattias Beck, Jérôme Faist, Giacomo Scalari
5 min
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 sub-wavelength 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.
Alex: One focused gate instead of arrays makes sense for tiny scales. Does a new feature called the M1 mode tie back to the squeeze?
Sam: Yes—the M1 mode appears as a new peak up to 280 gigahertz, shifting higher with more voltage. The voltage imprints the loop's shape onto the electron layer, squeezing it into a narrow channel that traps waves inside.
Sam: Like water sloshing in a shallow puddle shaped by a cookie cutter—the confinement creates standing patterns that mix with the hybrid mode.
Alex: So the channel narrowing sparks these trapped waves that alter the spectrum. And simulations match the data?
Sam: Exactly—they simulated the channel narrowing from 0.92 micrometers at low bias to 0.41 at high. Polariton maps with those widths line up closely with real transmission peaks.
Alex: That bridges the voltage to fewer electrons and new waves. How do they pin down the electron count dropping nearly tenfold?
Sam: Two ways that align. First, from the measured coupling strength, which grows with the square root of electron number—like a team's total pull scaling with squad size in tug-of-war.
Sam: Second, an overlap factor measures how much the light's electric field lines up with the squeezed electrons—like shining a flashlight on a shrinking puddle, less gets lit up as it narrows.
Alex: Both methods agree on nearly tenfold fewer electrons?
Sam: Yes—from about 7900 at zero voltage to around 1400 at highest bias.
Alex: What's stopping them from squeezing even further?
Sam: Leakage currents through the thin insulator—electrons sneak past at higher voltages. Sharper etching or smaller resonators could push further.
Alex: Practical leaks set the floor, but the design confirms the mechanism solidly. This single-device tunability is a meaningful tool for probing few-electron light mixes.
Sam: Precisely. It opens controlled tests of hybrids in regimes arrays couldn't reach, verified from fields to fits. The evidence holds together well.
Alex: That's a meaningful advance for light-matter interactions at small scales. Thanks for breaking it down so clearly, Sam. Thanks for listening to ResearchPod.