Enhancing the Energy Resolution in Scanning Tunneling Microscopy: from dynamical Coulomb blockade to cavity quantum electrodynamics

TL;DR

This paper improves energy resolution in scanning tunneling microscopy at millikelvin temperatures by combining electromagnetic shielding and filtering, enabling the observation of Josephson coupling to cavity modes, bridging atomic and macroscopic quantum phenomena.

Contribution

It introduces a novel combination of shielding and filtering techniques that significantly enhances energy resolution and reveals coupling to cavity modes in STM.

Findings

Energy resolution improved to 3.7 μeV at 10 mK.

Coupling between Josephson current and cavity modes observed.

Enhanced sensitivity enables exploration of ultra-low-energy phenomena.

Abstract

Scanning tunneling microscopy and spectroscopy have become indispensable tools for probing condensed matter at atomic length scales, yet achieving ultimate energy resolution remains a persistent challenge. At mK temperatures, the dynamical Coulomb blockade regime fundamentally limits spectroscopic precision through energy exchange between tunneling electrons and the electromagnetic environment. Here, we demonstrate that combining local electromagnetic shielding with low-pass filtering directly at the cryogenic scan head improves the energy resolution by nearly an order of magnitude, reaching benchmark values as low as 3.7$\mu$eV at 10mK. We attribute this enhancement to efficient suppression of high-frequency radiation and capacitive shunting of the tunnel junction. Remarkably, this improved sensitivity reveals that the Josephson current couples to electromagnetic cavity modes of the centimeter-scale scan head, establishing a direct connection between atomic-scale tunneling processes and macroscopic cavity quantum electrodynamics. These advances open pathways for exploring ultra-low-energy phenomena with unprecedented precision.