'Wow' research: Quantum physics observed in ultrapure metals

Overview

Researchers of the Cluster of Excellence ct.qmat – Complexity and Topology in Quantum Matter have for the first time detected phenomena of quantum physics in ultrapure metals at the macroscopic level. Until now, most quantum effects could only be observed at the microscopic level in the world of atoms and electrons. By examining samples of the ultrapure metals palladium cobalt oxide (PdCoO₂) and platinum cobalt oxide (PtCoO2), the researchers were able to prove experimentally that the special laws of quantum physics in metals also apply on a larger scale. These spectacular research results were published in the scientific journal Science.
 
Every solid consists of an atomic lattice. In metals, electrons move through this lattice when electric current flows. However, even pure metals are contaminated with atoms foreign to the material, so that the electrons are deflected in their flow by a defect about every ten to hundred atoms. Almost ten years ago, researchers at the Max Planck Institute for Chemical Physics of Solids in Dresden discovered that the materials PtCoO₂ and PdCoO₂ from the Delafossite class of materials conduct electricity incredibly well. PdCoO₂ is still considered the best electrical conductor at room temperature ever discovered. Now, the same research group, led by Andrew Mackenzie and Philip Moll in collaboration with, among others, theoreticians from the Max Planck Institute for the Physics of Complex Systems Dresden have shown that this purity leads to completely new signatures of quantum physics in this material.
 
Electrons in metals behave like waves on the microscale, i.e., they can superimpose themselves and create periodic “patterns” – known as interference. However, this interference is disturbed by deflection at defect atoms: a defect blurs the wave front and the waves become incoherent. This happens about every ten to one hundred atoms. By measuring the conductivity of PtCoO₂ and PdCoO₂ in a magnetic field, the cluster researchers have now been able to demonstrate the periodic superposition of electron waves up to remarkable 20,000 interatomic bond lengths. This corresponds to about 0.01 millimetres and can almost be observed with the eye. Only the remarkable purity of the “delafossites” makes such coherent wave phenomena possible which could also have applications in information technology or quantum computers in the future.
 
“What the fellow researchers have observed in their experiment is a spectacular discovery for solid-state physics. While it was clear that the laws of quantum physics apply on a small – nanometer – scale, they were measured here on a completely different level – a micrometer scale. The observation of macroscopic quantum coherence in a metal opens up new fields of research for physicists from all over the world. This is a great success for the colleagues and the cluster of excellence ct.qmat,” comments the spokesperson of the Dresden cluster site, Prof Matthias Vojta.
 
Since 2019, ct.qmat has been a scientific collaboration between the University of Würzburg and TU Dresden, closely linked to the cutting-edge research of the five renowned non-university institutes: Helmholtz-Zentrum Dresden-Rossendorf, Leibniz Institute for Solid State and Materials Research Dresden, Max Planck Institute for Chemical Physics of Solids Dresden, the Max Planck Institute of Physics of Complex Systems Dresden and Bavarian Center for Applied Energy Research.
 
Click here for more details and contacts
 
Click here for the Science paper

Picture: Scanning electron microscope image of the ultrapure metal palladium cobat oxide PdCoO₂ © MPI CPfS