The Strange Metal Phase And Its Implications For Superconductivity

The behavior of electrons and the exact fundamentals underlying the phenomenon we call ‘electricity’ are still the subject of many competing theories and heated debates. This is most apparent in the area of superconducting research, where the Fermi liquid theory — which has has formed the foundation of much of what we thought we knew about interacting fermions and by extension electrons in a metal — was found to break down in cuprates as well as in other metals which feature a state that is a non-Fermi liquid, also called a ‘strange metal phase’.

This phase was the subject of a 2023 research article by [Liyang Chen] and colleagues in Science titled Shot Noise in a Strange Metal. As summarized in a Quanta Magazine article, the term ‘shot noise’ refers hereby to the quasiparticles that are postulated by the Fermi liquid theory to form part of the electrical current as electrons interact and ‘clump’ together, creating discrete ‘particles’ that can be measured like rain drops falling on a roof. [Liyang Chen] and colleagues created a 200 nm thin nanowire (pictured, top) out of ytterbium, rhodium and silicon, followed by cooling it down to a few Kelvin and measuring the current.

What the team found was no sign of these discrete quasiparticles, but rather non-Fermi liquid continuous current. Yet what is exactly the nature of this measured current? Quite a few attempts at explaining this phenomenon have been undertaken, e.g. Jianfan Wang et al. (2022) in rare-earth intermetallic compounds. More recently [Riccardo Arpaia] and colleagues explore charge density fluctuations (CDF) as a signature of the quantum critical point (QCP), which is a point in the phase diagram where a continuous phase transition takes place at absolute zero.

They studied the CDF using X-ray scattering in cuprate superconductors with a wide doping range, using the measured CDF as an indication of the QCP, indicating that the former may be a result of the latter. With these results mostly inspiring more discussion and research, it’ll probably be a while still before we risk replacing the Fermi liquid theory, or apply strange metal findings to produce high-temperature superconductors.

Ask Hackaday: What If You Did Have A Room Temperature Superconductor?

The news doesn’t go long without some kind of superconductor announcement these days. Unfortunately, these come in several categories: materials that require warmer temperatures than previous materials but still require cryogenic cooling, materials that require very high pressures, or materials that, on closer examination, aren’t really superconductors. But it is clear the holy grail is a superconducting material that works at reasonable temperatures in ambient temperature. Most people call that a room-temperature superconductor, but the reality is you really want an “ordinary temperature and pressure superconductor,” but that’s a mouthful.

In the Hackaday bunker, we’ve been kicking around what we will do when the day comes that someone nails it. It isn’t like we have a bunch of unfinished projects that we need superconductors to complete. Other than making it easier to float magnets, what are we going to do with a room-temperature superconductor? Continue reading “Ask Hackaday: What If You Did Have A Room Temperature Superconductor?”

Evidence For Graphite As A Room Temperature Superconductor

Magnetization M(H) hysteresis loops measured for the HOPG sample, before and after 800 K annealing to remove ferromagnetic influences. (Credit: Kopelevich et al., 2023)
Magnetization M(H) hysteresis loops measured for the HOPG sample, before and after 800 K annealing to remove ferromagnetic influences. (Credit: Kopelevich et al., 2023)

Little has to be said about why superconducting materials are so tantalizing, or what the benefits of an ambient pressure, room temperature material with superconducting properties would be. The main problem here is not so much the ‘room temperature’ part, as metallic hydrogen is already capable of this feat, if at pressures far too high for reasonable use. Now a recent research article in Advanced Quantum Technologies by Yakov Kopelevich and colleagues provides evidence that superconducting properties can be found in cleaved highly oriented pyrolytic graphite (HOPG). The fact that this feat was reported as having been measured at ambient pressure and room temperature makes this quite noteworthy.

What is claimed is that the difference from plain HOPG is the presence of parallel linear defects that result from the cleaving process, a defect line in which the authors speculate that the strain gradient fluctuations result in the formation of superconducting islands, linked by the Josephson effect into Josephson junctions. In the article, resistance and magnetization measurements on the sample are described, which provide results that provide evidence for the presence of these junctions that would link superconducting islands on the cleaved HOPG sample together.

As with any such claim, it is of course essential that it is independently reproduced, which we are likely to see the results of before long. An interesting part of the claim made is that this type of superconductivity in linear defects of stacked materials could apply more universally, beyond just graphite. Assuming this research data is reproduced successfully, the next step would likely be to find ways to turn this effect into practical applications over the coming years and decades.

Another Room-Temperature Superconductivity Claim And Questions Of Scientific Integrity

In early March of 2023, a paper was published in Nature, with the researchers claiming that they had observed superconductivity at room temperature in a conductive alloy, at near-ambient pressure. While normally this would be cause for excitement, what mars this occasion is that this is not the first time that such claims have been made by these same researchers. Last year their previous paper in Nature on the topic was retracted after numerous issues were raised by other researchers regarding their data and the interpretation of this that led them to conclude that they had observed superconductivity.

According to an interview with one of the lead authors at the University of Rochester – Ranga Dias – the retracted paper has since been revised to incorporate the received feedback, with the research team purportedly having invited colleagues to vet their data and experimental setup. Of note, the newly released paper reports improvements over the previous results by requiring even lower pressures.

Depending on one’s perspective, this may either seem incredibly suspicious, or merely a sign that the scientific peer review system is working as it should. For the lay person this does however make it rather hard to answer the simple question of whether room-temperature superconductors are right around the corner. What does this effectively mean?

Continue reading “Another Room-Temperature Superconductivity Claim And Questions Of Scientific Integrity”

Room Temperature Superconductor? Yes, But Not So Fast…

There’s good news and there’s bad news in what we’re about to tell you. The good news is that a team of physicists has found a blend of hydrogen, carbon, and sulfur that exhibit superconductivity at 59F. Exciting, right? The bad news is that it only works when being crushed between two diamonds at pressures approaching that of the Earth’s core. For perspective, the bottom of the Marianas trench is about 1,000 atmospheres, while the superconductor needs 2.6 million atmospheres of pressure.

Granted, 59F is a bit chilly, but it is easy to imagine cooling something down that much if you could harness superconductivity. We cool off CPUs all the time. However, unless there’s a breakthrough that allows the material to operate under at least reasonable pressures, this isn’t going to change much outside of a laboratory.

Continue reading “Room Temperature Superconductor? Yes, But Not So Fast…”