An ultracompact scanning tunneling microscope within a Φ 10 piezo tube in a 20 T superconducting magnet.

ABSTRACT

Low-temperature scanning tunneling microscopy and spectroscopy (STM/S) help to better understand the fundamental physics of condensed matter. We present an ultracompact STM within a Φ 10 piezo tube in a 20 T superconducting magnet. The carefully cut piezo tube contains the STM's coarse-positioning assembly. Loading an STM tip-sample mechanical loop into the piezo tube with special cut openings enables an ultracompact pencil-size dimension down to Φ 10 mm, in which fine-machined nonmagnetic parts are assembled to enable slide-stick motion and xyz-scanning procedures. The small size leads to a higher resonant frequency, a typical feature of a rigid STM instrument, increasing its vibration immunity. Scanning by moving the sample while keeping the tip stationary improves the stability of the tip-sample junction compared to moving the tip. Taking advantage of its high-field compatibility and rigid design, our STM captures the atomically resolved topography of highly oriented pyrolytic graphite (HOPG) at 1.5 K and in magnetic fields up to 17 T. The topography of graphene lattice and graphite is simultaneously recorded on an atomic terrace of HOPG, unveiling a modified local charge density at a surface defect. The superconducting energy gaps of layered type-II superconductors NbSe2 and PdBi2 are well resolved through dI/dV tunneling spectra at sub-2 K. Our unique STM is highly suitable for potential STM/S applications in world-class high-field facilities where the strong magnetic field can exceed 30 T.