Our theoretical understanding of the way metals conduct electricity is incomplete. The current classification appears to be too vague and contains too many exceptions which makes it compelling. This is the conclusion reached by material scientists from the University of Groningen after a thorough examination of the recent literature on minerals. They analyzed more than 30 minerals and showed that a simple formula can provide a more systematic classification of minerals. Their analysis was published in physical review b On August 29.
Metals conduct electricity, but not all of them do the same. Scientists distinguish several classes of minerals with names such as “associated”, “normal”, “strange” or “ad”. Metals in these classes differ, for example, in the way their resistance responds to increasing temperatures. “We were interested in metals that can change from conductor to insulator and vice versa,” explains Beatrice Noheda, professor of functional nanomaterials at the University of Groningen. She is the scientific director of the CogniGron Research Center, which develops material-focused systems models for cognitive computing. “For this purpose, we would like to make materials that can not only be insulators or conductors, but can also change between those countries.”
When studying literature metal resistance, she and her colleagues found that the demarcation between the different metal classes was not straightforward. “So, we decided to take a look at a large sample of minerals.” Qikai Guo – a former postdoctoral researcher on the Noheda team and now at the School of Microelectronics at Shandong University, China – and their colleagues from the University of Zaragoza (Spain) and CNRS (France) used the change in resistance at higher temperatures as a comparison tool over 30 metals, based in part to literature data and partly based on their own measurements.
“The theory states that the resistance response is dictated by the scattering of electrons and that there are different scattering mechanisms at different temperatures,” Nohida explains. For example, at very low temperatures, a quadratic increase is found, which is said to be the result of electron scattering. However, some materials (“strange” metals) exhibit strict linear behavior that is not yet fully understood. Electron-phonon scattering was thought to occur at higher temperatures and this leads to a linear increase. However, dispersion cannot increase indefinitely, which means that saturation must occur at a certain temperature. “However, some minerals do not show any saturation in the measurable temperature range and have been referred to as ‘bad’ metals,” says Nohida.
When analyzing the responses of different types of minerals to higher temperatures, Nohida and her colleagues encountered something unexpected: “We can fit all data sets to the same type of equation.” It turns out that this is the Taylor extension, where resistance r is described as r = r0 +1T + A2T2 +3T3… , where T is a file temperaturewhile p0 And different A values are different constants. “We have found that using only a linear and quadratic term is sufficient to produce a very good fit for all metals,” explains Noheda.
In the paper, it is shown that the behavior in different types of minerals is determined by the relative importance of A.1 and2 and size r0. Noheda says, “Our formula is a purely mathematical description, without any physical assumptions, and depends on only two factors.” This means that linear and quadratic systems do not describe different mechanisms, such as electron-phonon and electron-electron scattering, they represent only linear (through incoherent dissipation, where the electron wave phase is changed by scattering) and non-linear coherent (where phase is not changed) contributions dispersion;
In this way, one equation can describe the resistance of all metals – whether they are natural, correlated, bad, exotic, or otherwise. The advantage is that all minerals can now be classified in a simple way that is more transparent to non-experts. But this description also brings another bonus: it shows that the term linear dissipation at low temperatures (called Planck dissipation) appears in all metals. This universality is something that others have already alluded to, but this formulation clearly shows that this is indeed the case.
Nohida and her colleagues are not mineralogists. “We came from outside the field, which means we took a fresh look at the data. What went wrong, in our opinion, is that people searched for meaning and mechanisms associated with linear and quadratic terms. Perhaps, some of the conclusions drawn in this way need to be revised. It is known that the theory In this incomplete area.” Noida and her colleagues hope so Theoretical physicists He will now find a way to reinterpret some of his previous results thanks to the formula they found. “But in the meantime, our purely phenomenological description allows us to compare minerals of different classes.”
Qikai Guo et al, Phenomenological classification of minerals based on resistance, physical review b (2022). DOI: 10.1103/ PhysRevB.106.085141
University of Groningen
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