1. Reports

2. Theories

3. References

A room-temperature superconductor is a material that is capable of exhibiting superconductivity at operating temperatures above 0 °C (273.15 K). While this is not strictly "room temperature", which would be approximately 20–25 °C, it is the temperature at which ice forms and can be reached and easily maintained in an everyday environment. In February 2019, US Navy filed a patent claiming that a room-temperature superconductivity can be achieved using a wire with an insulator core and an aluminum lead zirconate titanate. Another high temperature superconducting material is highly pressurized hydrogen sulfide, the transition temperature of which is {{convert|203|K|°C}}, the highest accepted superconducting critical temperature as of 2015.^[1] By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C and achieve room-temperature superconductivity.^[1] Previously the record was held by the cuprates, which have demonstrated superconductivity at atmospheric pressure at temperatures as high as {{convert|138|K|°C}}, and {{convert|164|K|°C}} under high pressure.^[2]

Although some researchers doubt whether room-temperature superconductivity is actually achievable,^[3][4] superconductivity has repeatedly been discovered at temperatures that were previously unexpected or held to be impossible.

Claims of "near-room temperature" transient effects date from the early 1950s and some suggest that in fact the breakthrough might have been made more than once but could not be made stable enough and/or reproducible as the relationship between isotope number and T_c was not known at the time.

Finding a room temperature superconductor "would have enormous technological importance and, for example, help to solve the world’s energy problems, provide for faster computers, allow for novel memory-storage devices, and enable ultra-sensitive sensors, among many other possibilities."^[4][5]

Reports

Since the discovery of high-temperature superconductors, several materials have been reported to be room-temperature superconductors, although none of these reports has been confirmed.

In 2000, while extracting electrons from diamond during ion implantation work, Johan Prins claimed to have observed a phenomenon that he explained as room-temperature superconductivity within a phase formed on the surface of oxygen-doped type IIa diamonds in a {{nowrap|10⁻⁶ mbar}} vacuum.^[6]

In 2003, a group of researchers published results on high-temperature superconductivity in palladium hydride (PdH_x: x>1)^[7] and an explanation in 2004.^[8]

In 2007 the same group published results suggesting a superconducting transition temperature of 260 K.^[9] The superconducting critical temperature increases as the density of hydrogen inside the palladium lattice increases. This work has not been corroborated by other groups.

In 2012, an Advanced Materials article claimed superconducting behavior of graphite powder after treatment with pure water at temperatures as high as 300 K and above.^[10][Unreliable source] So far, the authors have not been able to demonstrate the occurrence of a clear Meissner phase and the vanishing of the material's resistance.

In 2014, an article published in Nature suggested that some materials, notably YBCO (yttrium barium copper oxide), could be made to superconduct at room temperature using infrared laser pulses.^[11]

In 2015, an article published in Nature by researchers of the Max Planck Institute suggested that under certain conditions such as extreme pressure H₂S transitioned to a superconductive form H₃S at around 1.5 million times atmospheric pressure in a diamond anvil cell. The critical temperature is 203 K which would be the highest T_c ever recorded and their research suggests that other hydrogen compounds could superconduct at up to 260 K which would match up with the original research of Ashcroft.^[1][12]

In 2018, Dev Kumar Thapa and Anshu Pandey from the Solid State and Structural Chemistry Unit of the Indian Institute of Science in Bangalore claimed the observation of superconductivity at ambient pressure and room temperature in films and pellets of a nanostructured material that is composed of silver particles embedded in a gold matrix.^[13] Due to similar noise patterns of supposedly independent plots and the publication's lack of peer review, the results have been called into question.^[14]

Also in 2018, researchers noted a possible superconducting phase at {{convert|260|K|C}} in lanthanum decahydride at elevated (200 GPa) pressure.^[15]

Other research also suggests a link between the palladium hydride containing small impurities of sulfur nanoparticles as a plausible explanation for the anomalous transient resistance drops seen during some experiments, and hydrogen absorption by cuprates has been suggested in light of the recent results in H₂S as a plausible explanation for transient resistance drops or "USO" noticed

in the 1990s by Chu et al during research after the discovery of YBCO.{{CN|date=September 2016}}^[16]

It is also possible that if the bipolaron explanation is correct then under some conditions a normally semiconducting material can transition into a superconductor if a critical level of alternating spin coupling in a single plane within the lattice is exceeded.

The best analogy here would be anisotropic magnetoresistance^[17]{{Better source|reason=per WP:CIRCULAR|date=March 2019}} but in this case the outcome is a drop to zero rather than a decrease within a very narrow temperature range for the compound(s) tested.

Further support for anomalous spin states is found in^[18] though YPtBi is a relatively low temperature material it does suggest proof of concept.

In February 2019 a US Army patent reported that a piezoelectric wire showed zero electrical resistance.^[19]

Theories

Theoretical work by Neil Ashcroft predicted that solid metallic hydrogen at extremely high pressure (~500 GPa) should become superconducting at approximately room-temperature because of its extremely high speed of sound and expected strong coupling between the conduction electrons and the lattice vibrations (phonons).^[20] This prediction is yet to be experimentally verified, as yet the pressure to achieve metallic hydrogen is not known but may be of the order of 500 GPa.

A team at Harvard has claimed to make metallic hydrogen and reports a pressure of 495 GPa.^[21] Though the exact critical temperature has not yet been determined, weak signs of a Meissner effect at 250K may have appeared in magnetometer tests.

In 1964, William A. Little proposed the possibility of high temperature superconductivity in organic polymers.^[22] This proposal is based on the exciton-mediated electron pairing, as opposed to phonon-mediated pairing in BCS theory.

A variant of the resonating valence bond hypothesis has been suggested by several researchers including^[23] as an alternative explanation in the known cases where BCS breaks down. It is also possible that both are equally valid but just as with electronics the ohmic versus active model^[24] one can calculate an absurd result which shows that the other model is more likely to be correct.

As such a unified theory may need to use two or even three different models to explain all observed cases.

It has been further developed into an Ohm's Law like triangle with carrier variables suggesting which model to use based on experimental

results, and existing known superconductors being placed on a periodic table like arrangement.

This was suggested by A de Guerin around early 2019 and is the subject of a scientific paper which is being compiled for release.

References

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