Scattering-type scanning near-field optical microscopy with Akiyama piezo-probes

Abstract

Recent developments of the scattering-type scanning near-field optical microscope at cryogenic temperatures (cryogenic s-SNOM or cryo-SNOM) have led to many breakthroughs in the studies of low energy excitations in quantum materials. However, the simultaneous demands on vibration isolation, low base temperature, precise nano-positioning, and optical access make the construction of a cryo-SNOM a daunting task. Adding to the overhead space required for a cryo-SNOM is the atomic force microscopy control, which predominantly utilizes a laser-based detection scheme for determining the cantilever tapping motion. In this work, we provide an alternative and straightforward route to performing s-SNOM using metal-coated Akiyama probes, where the cantilever tapping motion is detected through a piezoelectric signal. We show that the Akiyama-based cryo-SNOM attains high spatial resolution, good near-field contrast, and is able to perform imaging with a significantly more compact system compared to other cryo-SNOM implementations. Our results firmly establish the potential of s-SNOM based on self-sensing piezo-probes, which can easily accommodate far-infrared wavelengths and high magnetic fields in the future.

Infrared nano-imaging of Dirac magnetoexcitons in graphene

“…As such, the largest cyclotron energy gap at a given magnetic field is apparently attained in quantum materials with a linear energy-momentum techniques that involve the confinement of light to nanoscale dimensions matching the momentum and wavelength of the collective mode of interest 17,18 . Here we report a visualization of the DiMEs and a previously unreported mapping of the DiME dispersion at infrared frequencies using a home-built cryogenic magneto scanning near-field optical microscope (m-SNOM) 19 . By coupling light resonantly to the inter-LL transitions, we observed magnetic-field-tunable DiME signatures in the scattered m-SNOM signal and an accompanying photocurrent modulation at the edges of graphene.…”

Analysis of Near-Field Magnetic Responses on ZrTe5 through Cryogenic Magneto-THz Nano-Imaging

“…Another challenge comes the development of THz sources and detectors capable of accessing a broadband THz range [23,24]. In recent years, there have been many systems that have enabled progress towards this goal [25][26][27][28][29][30], including a recent study utilizing high magnetic fields at infrared frequencies [31]; however, such a nano-THz microscope under these conditions has only recently been achieved [32].…”