Ultrabroadband Terahertz Near-Field Nanospectroscopy with a HgCdTe Detector
Lukas Wehmeier, Mengkun Liu, Suji Park, Houk Jang, D. N. Basov, C. C. Homes, G. L. Carr
Abstract
High Resolution Image Download MS PowerPoint Slide While near-field infrared nanospectroscopy provides a powerful tool for nanoscale material characterization, broadband nanospectroscopy of elementary material excitations in the single-digit terahertz (THz) range remains relatively unexplored. Here, we study liquid-Helium-cooled photoconductive Hg 1– X Cd X Te (MCT) for use as a fast detector in near-field nanospectroscopy. Compared to the common T = 77 K operation, liquid-Helium cooling reduces the MCT detection threshold to ∼22 meV, improves the noise performance, and yields a response bandwidth exceeding 10 MHz. These improved detector properties have a profound impact on the near-field technique, enabling unprecedented broadband nanospectroscopy across a range of 5 to >50 THz (175 to >1750 cm –1, or <6 to 57 μm), i.e., covering what is commonly known as the “THz gap”. Our approach has been implemented as a user program at the National Synchrotron Light Source II, Upton, USA, where we showcase ultrabroadband synchrotron nanospectroscopy of phonons in ZnSe (∼7.8 THz) and BaF 2 (∼6.7 THz), as well as hyperbolic phonon polaritons in GeS (6–8 THz).