A room-temperature superconductor is a hypothetical material that exhibits superconductivity at operating temperatures above 0° C (273.15 K) which, though not "room temperature" (approx. 20–25 °C) is the temperature at which ice forms and can be reached and easily maintained in an everyday environment. The highest temperature known superconducting materials are the cuprates, which have demonstrated superconductivity at atmospheric pressure at temperatures as high as -135 °C (138 K).
Although research into room-temperature superconductivity may produce no result, superconductivity has repeatedly been discovered at temperatures that were previously unexpected or held to be impossible.
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 10-6 mbar vacuum.
In 2003, a group of researchers published results on high-temperature superconductivity in palladium hydride (PdHx: x>1) and an explanation in 2004. In 2007 the same group published results suggesting a superconducting transition temperature of 260 K. 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 describes superconducting behavior of graphite powder after treatment with pure water at temperatures as high as 300 K and above. So far, the authors have not been able to prove vanishing of the material's resistance.
In 2013 an article published by Yasushi Kawashima describes the observation of circulating currents in a ring shaped container of highly ordered pyrolytic graphite (HOPG) soaked in either n heptane or octane which suggests the presence of a superconductive state.
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). 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.
In 1964, William A. Little proposed the possibility of high temperature superconductivity in organic polymers. This proposal is based on the exciton-mediated electron pairing, as opposed to phonon-mediated pairing in BCS theory.
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