Science has a problem with superconductivity at room temperature

One of the most important studies on the subject of superconductivity at room temperature - considered by many to be the holy grail of physics, the one that would allow us to optimize the production and distribution of energy - has just been withdrawn from Nature, the journal in which it was published. in 2020. The publisher motivated the choice by citing all the doubts raised by various scientists about the legitimacy of the results. Perplexities which, as we will see shortly, have resulted in one of the most heated and controversial discussions in recent years. "For some time - said James Hamlin, an experimental physicist expert in condensed matter at the University of Florida - there have been many objections to these results". Jorge Hirsch, another expert at the University of California, San Diego, one who certainly does not send them to say (we will see this too shortly), has increased the dose, saying that the withdrawal of the article is not enough since the team di Randa would have consciously manipulated the data: "I think this is a problem of scientific misconduct, which cannot be dismissed as a simple 'difference of opinion'".

Superconductivity, history and context

Let's go in order. Until the beginning of the last century it was known that under "normal" conditions (in this case with respect to temperature) any material in which electric current flows has a sort of "friction" - the so-called resistance - to the passage of charge carriers, which among other things leads to the development of heat by virtue of the so-called Joule effect. In other words, under normal conditions the flow of electrons (ie the electric current) is "hindered" inside the conductor, and loses a certain amount of energy.

Things changed in 1911, when the Dutch physicist Heike Kamerlingh Onnes discovered that in particular conditions, i.e. when the temperature approaches absolute zero, the resistance of some materials suddenly zeroes: these materials are transformed into superconductors and charge carriers flow through it without dissipating energy by friction.

In the last century the scientific community - both theorists and experimentalists - has worked hard to understand the mechanism of superconductivity, focusing mainly on 'goal of replicating the phenomenon at room temperature. If you really want to exploit the "revolutionary" advantage of superconductivity - carry current in a much better way, without dissipating energy and thus improving the efficiency of distribution by various factors - you have to try to replicate it at room temperature: it is in fact impossible to think of distributing current at temperatures close to absolute zero, a scenario that at the moment can only be created in a controlled laboratory environment.

One of the most interesting researches of recent years on the subject of superconductivity at room temperature bears the signature of a team of scientists from the Indian Institute of Science, who announced in June 2019 that they had developed a new nanomaterial based on silver particles encapsulated in a matrix of gold atoms that would transform into a superconductor at temperatures well beyond zero absolute.

The controversy

Shortly after, however, the American physicist Brian Skimmer a announced that he had identified, in the data of the Indian researchers, a recurrent and suspected pattern of noise present both in the samples analyzed and in those used as controls, which could indicate an error in the interpretation of the results or even a bad faith manipulation of the data.

This is how we come to the present: in 2020 in Science an editorial with the unequivocal title is published: "Superconductivity at room temperature is finally obtained: an experiment by another team of scientists (whose details were published in Nature), coordinated by Ranga Dias, a physicist at the University of Rochester, who claims to be able to synthesize a material composed of a mix of hydrogen, carbon and sulfur capable of showing superconductivity characteristics at room temperature, provided however, to be subjected to very high pressures, equal to about 2 million and a half the atmospheric pressure. From a practical point of view, it is as if the difficulty had shifted from reaching absolute zero (roughly) to reaching very high pressures.

As we said at the beginning, Dias's work has also been the subject of strong disputes: Hirsch has repeatedly asked - obtaining very spicy refusals - to check the data of the experiment, coming to the conclusion that the results are "probably fraudulent". The escalation of the discussion led to the suspension for six months of Hirsch's account from ArXiv, the portal on which scientific articles are uploaded before their actual publication in a journal and which should serve, precisely, to a profitable and peaceful discussion among experts.

What happened today

Following all these controversies, the Board of Nature has decided to withdraw the article from the Dias team. Which, of course, does not fit: "Our work - he commented - has been verified experimentally and theoretically". "The withdrawal of the article - echoes Ashkan Salamat, physicist at the University of Nevada, Las Vegas and co-author of the work - is not due to doubts about the decrease in electrical resistance, the truly fundamental part of any work on superconductivity. We are confused and disappointed by the decision-making process of the editors of Nature ".

The point is that to prove the existence of such a delicate and complex phenomenon, experts in favor of the withdrawal of the article say, it is not enough to prove a decrease in electrical resistance: another crucial attribute of superconductors should also be shown, namely the ability to “expel” an external magnetic field after the transition to superconductivity. Since for technical reasons it is not always possible to quantify this capacity, the experimentalists evaluate it by measuring a correlated quantity, the so-called magnetic susceptibility - which is anything but simple: "It's like trying to see a star - explained Hamlin - under the light of the Sun ".

It is precisely the data relating to magnetic susceptibility that led to the withdrawal of Dias's study: the authors, in fact, affirmed that in their experiment signals emerged relating to an increase in susceptibility magnetic, but at first they did not want to show the data underlying the claim. In 2021, after the first controversies, they did so, but without convincing the detractors. Indeed, making the situation worse: “The publication of the raw data - commented Brad Ramshaw, a physicist at Cornell University - raised more questions than he answered. The process by which from the raw data to actually published data is incredibly opaque. ”

There's more: Hirsch argues that some of the data from Dias and Salamat are completely incompatible with what they would get in a real experiment, explaining that he is convinced that they were "artfully constructed" and that they are "suspiciously similar" to those contained in another article published in 2009 and, coincidentally, withdrawn last year due to inaccurate data on susceptibility magnetic. Dias, once again, disagrees: he claims he intends to send the article again (with some modifications) to Nature and accuses Hirsch of not being an expert in the field of high pressure physics: "Some of his actions have turned into personal attacks - he explains - and we don't want to have colleagues throwing mud at us from afar. We invite our colleagues to cease and desist from the controversy ”. We laymen just have to keep observing. And wait.