Infrared nanoscopy down to liquid helium temperatures

We introduce a scattering-type scanning near-field infrared microscope (s-SNIM) for the local scale near-field sample analysis and spectroscopy from room temperature down to liquid helium (LHe) temperature. The extension of s-SNIM down to T = 5 K is in particular crucial for low-temperature phase transitions, e.g., for the examination of superconductors, as well as low energy excitations. The low temperature (LT) s-SNIM performance is tested with CO2-IR excitation at T = 7 K using a bare Au reference and a structured Si/SiO2-sample. Furthermore, we quantify the impact of local laser heating under the s-SNIM tip apex by monitoring the light-induced ferroelectric-to-paraelectric phase transition of the skyrmion-hosting multiferroic material GaV4S8 at Tc = 42 K. We apply LT s-SNIM to study the spectral response of GaV4S8 and its lateral domain structure in the ferroelectric phase by the mid-IR to THz free-electron laser-light source FELBE at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Notably, our s-S...