Physicists make molecular vibrations more detectable

In molecules, the atoms vibrate with characteristic patterns and frequencies. Vibrations are therefore an important tool to study molecules and molecular processes such as chemical reactions. Although individual molecules can be imaged with scanning tunneling microscopes, their vibrations have so far been difficult to detect.

Physicists from the CAU (Christian-Albrechts-Universität zu Kiel, CAU) have now invented a method with which the vibration signals can be amplified by a factor of 50. They have also significantly increased the frequency resolution. The new method will improve the understanding of interactions in molecular systems and other simulation methods. The research team has now published the results in the specialist journal Physical Verification Letters.

The discovery of dr. Jan Homberg, Dr. Alexander Weismann and Prof. Dr. Richard Berndt from the Institute for Experimental and Applied Physics is based on a special quantum mechanical effect, the so-called “inelastic tunneling”. Electrons that pass a molecule on their way from a metal tip to the substrate surface in the scanning tunneling microscope can give off energy to the molecule or absorb energy from it. This exchange of energy occurs in portions determined by the properties of each molecule.

Normally, this transfer of energy occurs infrequently and is therefore difficult to measure. In order to amplify the measurement signal and at the same time achieve high frequency resolution, the CAU team used a previously discovered special property of molecules on superconductors: Appropriately arranged, the molecules in the spectra show a state that appears needle-like, very high and extremely sharp – the so-called Yu-Shiba-Rusinov resonance.

The experiments were supported by theoretical work by Troels Markussen from the software company Synopsis in Copenhagen.

Provided by the Christian-Albrechts-University in Kiel