Next-generation photonics and mobile networks are made possible by quantum materials in the terahertz range.
Terahertz light, which is radiation in the far-infrared region of the emission spectrum, is currently underutilised in technology despite having a wide range of potential uses in sensing, screening for domestic terrorism, and future (sixth generation) mobile networks.
Although this radiation has low photon energy and is therefore safe, it can nonetheless penetrate a wide variety of materials (such as skin, packaging, etc.). The wonder substance graphene is among the research groups that have concentrated on finding methods and materials to effectively generate THz electromagnetic waves in the last ten years, but it does not yield the expected outcomes. The generated terahertz output power in particular is constrained.
According to an article recently published in Light: Science & Applications, topological insulators (TIs), quantum materials that behave as insulators in the bulk while exhibiting conductive qualities on the surface, have now improved performance.
Members of the ICN2 Ultrafast Dynamics in Nanoscale Systems Group, directed by Dr. Klaas-Jan Tielrooij, and the High-field THz Driven Phenomena Group at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), directed by Dr. Sergey Kovalev, conducted this research in conjunction with scientists from the ICN2 Physics and Engineering of Nanodevices Group, directed by ICREA Prof. Sergio O (Germany). The TELBE THz facility in Dresden hosted the experiments.
According to earlier research, materials like the aforementioned graphene and topological insulators, which host electrons with zero effective mass, efficiently generate terahertz harmonics. When photons of the same frequency and energy interact non-linearly with matter, a process known as harmonic generation occurs. This causes the emission of photons with an energy that is several times greater than the incident photons. To upconvert electronically generated signals in the high GHz realm into signals in the THz regime, for instance, this can be used.
In direct contrast to a reference graphene sample, Dr. Tielrooij and associates examined the behaviour of two topological insulators, the archetypal Bi2Se3 and Bi2Te3.
They discovered that, unlike graphene, which is constrained by saturation effects (which appear at high incident powers), the maximum power of the harmonics created in these quantum materials increased with the incident fundamental power. The results of the studies showed that the generated output power was orders of magnitude more than graphene and was getting close to the milliwatt range.
The fact that topological insulators can rely on a highly effective cooling mechanism, in which the massless charges on the surface disperse their electronic heat to those in the rest of the thin film, is what causes this huge divergence in behaviour. In other words, by dissipating electronic heat, bulk electrons support surface-state electrons.
The metamaterial with the highest terahertz third-harmonic output power—radiation with three times the energy—also comprised a topological insulator film and a metallic grating, which is made up of metal strips spaced apart by gaps on the surface.
“In this work, we were able to show that topological insulators exhibit a substantially weaker saturation effect than does graphene. This happens because topological insulators’ surface and bulk electrons have a novel cooling mechanism “Dr. Klaas-Jan Tielrooij, the paper’s primary author, explains. These quantum metamaterials so advance the development of nonlinear terahertz photonics technology.
According to the paper’s final author, Sergey Kovalev, “the acquired results further offer exciting opportunities towards exploring the quantum features of these materials with prospects towards quantum technology.”
Find More: Klaas-Jan Tielrooij et al, Milliwatt terahertz harmonic generation from topological insulator metamaterials, Light: Science & Applications (2022). DOI: 10.1038/s41377-022-01008-y
