Amplifier for scanning tunneling microscopy at MHz frequencies

TL;DR

This paper introduces a novel MHz-frequency amplifier for scanning tunneling microscopy, enabling high-speed measurements while maintaining atomic resolution, with potential applications in quantum physics and spin resonance detection.

Contribution

The authors develop and test a high-Q LC tank amplifier with low-noise HEMT for MHz STM measurements, surpassing conventional bandwidth limitations.

Findings

Successful spatial mapping of tunneling electron noise on Au(111)

Differential conductance spectroscopy at 3MHz shows improved performance

Amplifier design compatible with ultra-high vacuum and low temperature conditions

Abstract

Conventional scanning tunneling microscopy (STM) is limited to a bandwidth of circa 1kHz around DC. Here, we develop, build and test a novel amplifier circuit capable of measuring the tunneling current in the MHz regime while simultaneously performing conventional STM measurements. This is achieved with an amplifier circuit including a LC tank with a quality factor exceeding 600 and a home-built, low-noise high electron mobility transistor (HEMT). The amplifier circuit functions while simultaneously scanning with atomic resolution in the tunneling regime, i.e. at junction resistances in the range of giga-ohms, and down towards point contact spectroscopy. To enable high signal-to-noise and meet all technical requirements for the inclusion in a commercial low temperature, ultra-high vacuum STM, we use superconducting cross-wound inductors and choose materials and circuit elements with low heat load. We demonstrate the high performance of the amplifier by spatially mapping the Poissonian noise of tunneling electrons on an atomically clean Au(111) surface. We also show differential conductance spectroscopy measurements at 3MHz, demonstrating superior performance over conventional spectroscopy techniques. Further, our technology could be used to perform impedance matched spin resonance and distinguish Majorana modes from more conventional edge states.