A new compact closed-cycle cryocooler system for variable temperature nano-imaging and -spectroscopy

Scanning nano-optical imaging and -spectroscopy have emerged as powerful tools in investigating and understanding heterogeneities and associated physics in a wide range of organic, layered van der Waals, and correlated electron materials. However, to answer many fundamental questions and to access complex quantum phases requires cryogenic temperatures. Despite this need, the extension of optical nano-imaging to variable and low temperatures has remained a major experimental challenge. Here, we present from variable temperature infrared nano-imaging and spectroscopy (IR s-SNOM) to tip-enhanced photoluminescence and nano-Raman spectroscopy in different instruments based on closed cycle cryocoolers with an exchange gas cooled low vibration interface. At the example of surface plasmon polariton (SPP) nano-imaging of graphene, we establish IR nano-imaging at temperatures as low as 15 K with spatial resolution of 10 nm allowing us to access the fundamental limits of SPP propagation. Further, we demonstrate low-temperature TEPL and TERS of transition metal dichalcogenide (TMD) heterostructures to resolve different exciton degrees of freedom and their nanoscale strain control.