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High-performance THz sensing based on the strong THz nonlinear electrodynamics in a layered correlated topological semimetals TaIrTe 4 . Credit: Xin (Zoe) Zou
Terahertz radiation (THz), electromagnetic radiation with frequencies ranging between 0.1 and 10 THz, could be leveraged to develop various new technologies, including imaging and communication systems. So far, however, a lack of fast and sensitive detectors that can detect radiation across a wide range of frequencies has limited the development of these THz-sensing technologies.
In a recent paper published in Nature Electronics, researchers at the University of Wisconsin-Madison, the University of Tennessee and other institutes have introduced new photodetectors made of tantalum iridium telluride (TaIrTe₄), a 2D-correlated topological semimetal that exhibits advantageous properties. Most notably, this material exhibits a strong nonlinear Hall effect, a physical effect that entails a transverse voltage in the absence of an external magnetic field, which is nonlinearly proportional to an applied electric field or current.
"THz technology is critical in quantum information technology and biomedical sensing because its frequency resonates with low-energy collective excitations in quantum materials and molecular vibrations in biological matters," Jun Xiao, senior author of the paper, told Phys.org.
"Moreover, the ultra-high bandwidth of the THz band could enable desired high-speed wireless communication. However, the widespread application of THz technologies has been hindered due to the lack of simultaneous sensitive, broadband, and fast THz detection in state-of-the-art detectors such as thermal bolometers and electronic Schottky diodes."
Existing photodetectors capable of detecting THz radiation are either too slow, not sensitive enough, or only capable of detecting signals at some frequencies. Xiao and his colleagues thus set out to develop new photodetectors based on alternative materials, which could overcome the limitations of previously developed devices, exhibiting good sensitivity, fast speeds and broadband.
"We fabricated Har bar geometry sensing devices using atomically thin TaIrTe₄, a 2D-correlated topological semimetal, and exposed them to terahertz (THz) radiation," explained Xiao. "We characterized this effect by measuring THz-induced photocurrent and evaluating device performance metrics such as responsivity and sensitivity. To assess the response speed, we conducted ultrafast autocorrelation measurements using femtosecond laser-generated THz pulses, revealing intrinsic picosecond-scale dynamics."
As part of their study, Xiao and his colleagues also probed the crystal symmetry of TaIrTe₄ using a technique known as second-harmonic generation (SHG) spectroscopy. Using this technique, they observed the emergence of a correlated electronic phase at low temperatures that further enhanced their photodetectors' THz response, or in other words, improved their ability to quickly and precisely detect THz radiation.
"Additionally, we demonstrated that the sensing performance and electronic state could be tuned via electrostatic gating," said Xiao. "These combined methods revealed TaIrTe₄'s promise for fast, broadband, and highly sensitive room-temperature THz sensing."
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