Macroscopic quantum interference in an ultra-pure metal

June 12, 2020

That visible light holds the character of a wave can be demonstrated in simple optics experiments, or directly witnessed when rainbows appear in the sky. Although the subtle laws of quantum mechanics, that is, wave mechanics, ultimately govern all the processes of electron transportelectrons in solids, their wave-like nature of the electrons is not often apparent to the casual observer. A classical picture of electrons as solid particles goes surprisingly far in explaining electric currents in metals. As high school students see in experiments with water waves, and we observe and use with light waves in many optical devices, interference is a fundamental property associated with wave-like behavior. Indeed, Davisson and Germer’s famous observation of interference in experiments with dilute beams of electrons, nearly a century ago, gave key experimental support to the correctness of the then-new quantum theory.

In experiments on solids, however, signatures of quantum interference are rare and hard to observe.  This is essentially because there are so many electrons, and so many ways in which they can be ‘scrambled up’, that most interference effects are invisible to experiments that probe distances of more than a few atomic spacings.

The second derivative of the resistivity highlights the oscillatory part of the magnetoresistance. For this sample, an oscillation period of 1 Tesla was found.

One of the themes of research in the Physics of Quantum Materials department is the study of exotic strange layered metals from a structural class with the equally strange name ‘delafossites’, stemming from the famous French crystallographer Gabriel Delafosse.  They are notable because they conduct electricity incredibly well.  Indeed, at room temperature one of them, PtCoO2, is the best electrical conductor ever discovered. 

As part of the research on the delafossites, the dependence of the conduction perpendicular to the layers on magnetic field was studied, in crystals that had been sculpted into particular geometries using a focused ion beam. Strong oscillations in this conductivity were observed (see Figure). 

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