SUPERTERA · THz Near-Field Imaging of Unconventional Superconductors

THz Near-Field Imaging of Unconventional Superconductors

The SUPERTERA project is an exciting initiative aimed at advancing the technology of Terahertz (THz) waves, a part of the electromagnetic spectrum between microwaves and infrared light. THz waves have incredible potential, from improving medical imaging to developing quantum computers and advanced security systems. The project focuses on how these THz waves interact with superconductors—materials that can conduct electricity without resistance at very low temperatures. By understanding these interactions, we can create new technologies and devices with applications across healthcare, security, and electronics. Understanding Superconductors and THz Waves Superconductors are special materials that lose all electrical resistance when they are cooled to very low temperatures. High-temperature superconductors (high-Tc) are materials that become superconducting at higher temperatures than usual, though still extremely cold. These materials have many potential uses, but to fully unlock their potential, we need to understand how they behave when exposed to THz waves. In the SUPERTERA project, we used a special microscope called CryoSNOM that can study these superconductors at low temperatures and see how they respond to THz light. By exploring these interactions, the project aims to develop new ways of using THz waves for technology that could impact everything from quantum computers to medical scanners. The project was divided into several main objectives: 1. Studying Quantum Behaviors in Superconductors One of the first goals was to study a special quantum behavior called the "Higgs mode" in superconductors. This is a phenomenon where the superconducting state fluctuates, similar to how particles behave in the Higgs field. The challenge we faced was that superconductors have properties that make it difficult to see these effects with our microscope. Despite this, we have employed a technique called “photovoltage nanoscopy” which measures the tiny voltages created when THz light hits a material. Moreover, by employing THz CrySNOM (Near-Field Optical Microscope operating at temperatures as low as -265C) photovoltage hotspots could be mapped with nanometer precision. The formation of hotspots was tested on superconductors like NbN (a material that works at higher temperatures than others), using CryoSNOM and revealed how the THz light breaks down pairs of electrons that form the superconducting state. This process is key to developing better detectors for THz waves, which could be used in various technologies, including astronomy and medical imaging. By applying this technique, we created a new way to map how THz light interacts with superconductors, allowing us to see where and how the light affects the material. This was an important breakthrough and represents a major achievement of the project. 2. Exploring Magic-Angle Twisted Bilayer Graphene (MATBG) Another major focus was on a new and exciting material called Magic-Angle Twisted Bilayer Graphene (MATBG). This material is made by stacking two layers of graphene (an atom-thin form of carbon) at a very specific angle. MATBG can behave like a superconductor, and it has unique properties that make it a highly pursued topic in research today. Theory predicts that plasmons, which are waves of electric charge that move through the material play a role in the emergence of the superconducting properties in MATBG. For the first time, we were able to see these plasmons using CryoSNOM, providing valuable new insights into this material. 3. Adapting CryoSNOM for THz Technology To make these discoveries possible, the SUPERTERA team had to enhance the CryoSNOM setup, which was originally designed for infrared light. The team modified it to work with THz light, a key step that allowed us to study these materials in new ways. As a part of this endeavour a THz quantum cascade laser and a gas THz laser were coupled into the CryoSNOM path. This improvement was crucial for the majority of the steps in the project.

Data: CORDIS, © European Union