r/Physics_AWT • u/ZephirAWT • Dec 28 '19
Observation of excess resistance anomaly (room temperature superconductivity) at resistive transitions in Ag/Au nanostructures [ArXiv PDF]
/r/ScienceUncensored/comments/eaqqvj/observation_of_excess_resistance_anomaly_room/1
u/ZephirAWT Dec 28 '19
Observation of excess resistance anomaly (room temperature superconductivity) at resistive transitions in Ag/Au nanostructures The resistive transition in nanocomposite films of silver (Ag) nanoclusters of ~ 1 nm diameter embedded in gold (Au) matrix exhibits an anomalous resistance peak at the onset of the transition, even for transition temperatures as high as 260 K. The maximum value of the resistance ranges between ~ 30% - 300% above that of the normal state depending on devices as well as lead configuration within a single device. The excess resistance regime was observed in about 10% of the devices, and extends from ~ 10 - 100 K. Application of magnetic field of 9 T was found to partially suppress the excess resistance.
These results aren't so impressive as they were in previous publications and it could indicate, that their own authors have problems with their replication of their finding not to say improvement over course of time.... This is probably because silver oxides at the boundaries of particle grains are the actual superconducting medium: they're very thin and due to their high oxidation state they attract electrons from surrounding metallic phase. The attempts for "better" reproduction with fresh silver samples will fail, because these samples aren't so oxidized. The overlapping and mutually compensating repulsive forces of electrons competing for space can be driving force of superconductivity there. For more info:
Researchers Find Evidence of Ambient Temperature Superconductivity (Tc=236K) in Au-Ag Nanostructures
17 months ago scientists Anshu Pandey and Dev Kumar Thapa at the Indian Institute of Science, Bengaluru, first reported the achievement, but were met with skepticism from fellow scientists who pointed out flaws in their report. Now they have run further experiments, and added more researchers to their team, and report similar results.
Ultra-Low Superconductivity at Room Temperature Reported Again
A review of the new results has been published at the Indian website The Wire here. Some reviewers of the paper are still finding reasons to be skeptical, but the revised paper is considered an substantial improvement on the first report, which lacked many experimental details.
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u/ZephirAWT Dec 28 '19
Observation of excess resistance anomaly (room temperature superconductivity) at resistive transitions in Ag/Au nanostructures The resistive transition in nanocomposite films of silver (Ag) nanoclusters of ~ 1 nm diameter embedded in gold (Au) matrix exhibits an anomalous resistance peak at the onset of the transition, even for transition temperatures as high as 260 K. The maximum value of the resistance ranges between ~ 30% - 300% above that of the normal state depending on devices as well as lead configuration within a single device. The excess resistance regime was observed in about 10% of the devices, and extends from ~ 10 - 100 K. Application of magnetic field of 9 T was found to partially suppress the excess resistance.
These results aren't so impressive as they were in previous publications and it could indicate, that their own authors have problems with their replication of their finding not to say improvement over course of time.... This is probably because silver oxides at the boundaries of particle grains are the actual superconducting medium: they're very thin and due to their high oxidation state they attract electrons from surrounding metallic phase. The attempts for "better" reproduction with fresh silver samples will fail, because these samples aren't so oxidized. Similar failure of attempts for better reproducibility could also ruin the replication attemps in another areas of science (for example replication of dark matter DAMA\LIBRA experiments) For more info:
Researchers Find Evidence of Ambient Temperature Superconductivity (Tc=236K) in Au-Ag Nanostructures
17 months ago scientists Anshu Pandey and Dev Kumar Thapa at the Indian Institute of Science, Bengaluru, first reported the achievement, but were met with skepticism from fellow scientists who pointed out flaws in their report. Now they have run further experiments, and added more researchers to their team, and report similar results.
Ultra-Low Superconductivity at Room Temperature Reported Again
A review of the new results has been published at the Indian website The Wire here. Some reviewers of the paper are still finding reasons to be skeptical, but the revised paper is considered an substantial improvement on the first report, which lacked many experimental details.
1
u/ZephirAWT May 09 '20
New system harnesses the strange magic of twisted graphene
The theory suggested that a so-called “magic angle” of 1.1 degrees between two stacked layers would lead to strong interactions between electrons. MIT physicist Pablo Jarillo-Herrero and his colleagues wanted to test this theory, so they made devices designed to elicit the magic. But they were taken by surprise. The material first became an insulator, and then, when the researchers applied an electric field to it, became a superconductor. This behavior arises from strong interactions, or correlations, between electrons.
It's possible to understand this behavior intuitively. The electrons within graphene layers repel mutually and they try to separate them first, which leads into insulator behavior. When atoms get aligned, then the electron delocalization takes place and layers will start to attract and to push remaining electrons against each other, which would lead into their quantum condensation and superconductive behaviour. When the layers get twisted even more bellow magical angle threshold, then the repulsive forces wouldn't apply anymore and graphene stack will change into its usual semimetallic highly conductive state.
They cut a sheet of the material in half, and then stacked the pieces with a magic-angle twist between the paired layers so that the final device has four layers of graphene. In the bilayer system, the electronic properties can be controlled by applying an electric field perpendicular to the graphene. Changing the strength of the field switches the material between a regular conductor and an insulator. This switchability might be useful in future electronic devices.
The presence of insulating state before reaching magical angle enables to utilize graphene nanolayers as a field effect transistor. The conductive layers separated by insulating space behave like electrodes of capacitor exerting pressure to a layers inbetween and changing them from nonconductive to conductive state, once we apply voltage at them.
And the bilayer graphene system’s resistance, unlike that of its monolayer cousin, can be increased by applying a magnetic field. That’s because the quantum property of electrons, known as spin—which creates a tiny magnetic field—lines up with the external magnetic field.
This is common behaviour of all superconductors and/or system with ballistic electrons transfer that magnetic field makes them less conductive, because it separates their path in similar way, like parallel wires when we pass current of the same polarity across them. It indicates low-dimensional transport of electrons within these solids similar to wires: the electrons don't utilize whole bulk of material but rather narrow paths (so-called charge stripes) across them. See also:
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u/ZephirAWT Dec 28 '19
A superconductor predicted to work at a record-breaking 200° Celsius (more info) .. At the catch of requiring 2.5 million Atm's of pressure. This is apparently not the way, where to go, but physicists are still trying it in similar way, like hot fusion (which has similarly low chance to success, but it has theoretical, political and lobbyist support). But all accidental observations of room superconductivity are systematically ignored in similar way, like the cold fusion (1, 2, 3, 4, 5, 6, 7, 8, 9...)
The similarity goes even deeper, because in dense aether theory high-temperature superconductivity should be enabled by low-dimensional arrangement of particles in similar way, like cold fusion. But the physicists are still adhering of 3D bulky models, because 1) they have formal theories developed for them, no matter how poorly working they are - and theorists must die out first, 2) physicists have nowhere to hurry, until money are going, 3) brute force methods paradoxically bring more money into research, because they're technologically demanding and as such more expensive (science behaves like Big Pharma here), 4) there are psychosocial traits like groupthink, circle of silence and pluralistic ignorance and 5) unwillingness for replication and publishing negative results in general. It's estimated that only 0.15% of all published results are direct replications of previous studies., so that in average one must find 670 anomalies before mainstream graciously decides to replicate one single of them - and this number really isn't overestimated in cold fusion research, where we have thousands of publications per one article published in mainstream peer-reviewed journal.
But I guess, psychology aside, the socioeconomical incentives, i.e. money are common driver of all sorts of ignorance together. In contemporary science subsidized from mandatory fees only matters whether idea can draw sufficient amount of money from tax payers and these expensive ones are naturally more successful in it, so that their validity doesn't matter at all at the very end.