An atomic‐scale vector network analyzer

Abstract

Electronic devices have been ever‐shrinking toward atomic dimensions and have reached operation frequencies in the GHz range, thereby outperforming most conventional test equipment, such as vector network analyzers (VNA). Here the capabilities of a VNA on the atomic scale in a scanning tunneling microscope are implemented. Nonlinearities present in the voltage‐current characteristic of atoms and nanostructures for phase‐resolved microwave spectroscopy with unprecedented spatial resolution at GHz frequencies are exploited. The amplitude and phase response up to 9.3 GHz is determined, which permits accurate de‐embedding of the transmission line and application of distortion‐corrected waveforms in the tunnel junction itself. This enables quantitative characterization of the complex‐valued admittance of individual magnetic iron atoms which show a lowpass response with a magnetic‐field‐tunable cutoff frequency.