A room-temperature superconductor is a material that is capable of exhibiting
superconductivity
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlik ...
at
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
s above , that is, temperatures that can be reached and easily maintained in an everyday environment. , the material with the highest accepted superconducting temperature is an extremely pressurized
carbonaceous sulfur hydride with a critical transition temperature of +15 °C at 267 GPa.
On 22 September 2022, the original article reporting superconductivity in the carbonaceous sulfur hydride material was retracted by ''Nature'' journal editorial board due to a non standard, user-defined data analysis, calling into question the scientific validity of the claim.
At
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibar ...
the temperature record is still held by
cuprates, which have demonstrated superconductivity at temperatures as high as .
Although researchers once doubted whether room-temperature superconductivity was actually achievable,
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. 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."
[
]
Reports
Since the discovery of high-temperature superconductors, several materials have been reported to be room-temperature superconductors, although most of these reports have not been confirmed.
In 2000, while extracting electrons from diamond
Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, ...
during ion implantation
Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the physical, chemical, or electrical properties of the target. Ion implantation is used in semiconductor device fa ...
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 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 claimed superconducting behavior of graphite
Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...
powder after treatment with pure water at temperatures as high as 300 K and above. So far, the authors have not been able to demonstrate the occurrence of a clear Meissner Meissner, Meißner or Meisner may refer to:
Geography
Meissner is the name of the following geographic features:
* the Meißner (range), an important mountain range in Hesse, Germany
* Hoher Meißner, the highest peak of the Meißner range
* Meià ...
phase and the vanishing of the material's resistance.
In 2014, an article published in ''Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...
'' suggested that some materials, notably YBCO ( yttrium barium copper oxide), could be made to superconduct at room temperature using infrared laser pulses.
In 2015, an article published in ''Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...
'' by researchers of the Max Planck Institute suggested that under certain conditions such as extreme pressure transitioned to a superconductive form at 150GPa (around 1.5 million times atmospheric pressure) in a diamond anvil cell
A diamond anvil cell (DAC) is a high-pressure device used in geology, engineering, and materials science experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around ...
. The critical temperature is which would be the highest ''T''c ever recorded and their research suggests that other hydrogen compounds could superconduct at up to which would match up with the original research of Ashcroft.
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. Due to similar noise patterns of supposedly independent plots and the publication's lack of peer review
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a form of self-regulation by qualified members of a profession within the relevant field. Peer revie ...
, the results have been called into question. Although the researchers validated their findings in a later paper in 2019, this claim is yet to be verified and confirmed.
Also in 2018, researchers noted a possible superconducting phase at in lanthanum decahydride
Lanthanum decahydride is a polyhydride or superhydride compound of lanthanum and hydrogen (LaH10) that has shown evidence of being a high-temperature superconductor. It has a superconducting transition temperature TC ~ at a pressure of 150 gigapa ...
at elevated (200 GPa) pressure.
In 2019, the material with the highest accepted superconducting temperature was highly pressurized lanthanum decahydride
Lanthanum decahydride is a polyhydride or superhydride compound of lanthanum and hydrogen (LaH10) that has shown evidence of being a high-temperature superconductor. It has a superconducting transition temperature TC ~ at a pressure of 150 gigapa ...
(), whose transition temperature is approximately .
In October 2020, room-temperature superconductivity at 288 K (at 15 °C) was reported in a carbonaceous sulfur hydride at very high pressure (267 GPa) triggered into crystallisation via green laser. The paper has been retracted in 2022 as doubts were raised concerning the statistical methods used by the authors to derive the result.
In March 2021, an announcement reported room-temperature superconductivity in a layered yttrium-palladium-hydron material at 262 K and a pressure of 187 GPa.
Palladium may act as a hydrogen migration catalyst in the material.
Theories
Theoretical work by British physicist Neil Ashcroft predicted that solid metallic hydrogen
Metallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington.
At high pressure and temperatures, metallic hydro ...
at extremely high pressure (~500 GPa) should become superconducting at approximately room-temperature because of its extremely high speed of sound
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as ...
and expected strong coupling
A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end mov ...
between the conduction electrons and the lattice vibrations (phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...
s).[
] This prediction is yet to be experimentally verified, as the pressure to achieve metallic hydrogen is not known but may be on the order of 500 GPa.
A team at Harvard University
Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of high ...
has claimed to make metallic hydrogen and reports a pressure of 495 GPa. Though the exact critical temperature has not yet been determined, weak signs of a possible Meissner effect and changes in magnetic susceptibility at 250 K may have appeared in early magnetometer tests on the original now-lost sample and is being analyzed by the French team working with doughnut shapes rather than planar at the diamond culet tips.
In 1964, William A. Little proposed the possibility of high temperature superconductivity in organic polymers
A polymer (; Greek ''poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...
. This proposal is based on the exciton-mediated electron pairing, as opposed to phonon
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, specifically in solids and some liquids. A type of quasiparticle, a phonon is an excited state in the quantum mechanical ...
-mediated pairing in BCS theory
BCS theory or Bardeen–Cooper–Schrieffer theory (named after John Bardeen, Leon Cooper, and John Robert Schrieffer) is the first microscopic theory of superconductivity since Heike Kamerlingh Onnes's 1911 discovery. The theory describes su ...
.
In 2004, Ashcroft returned to his idea and suggested that hydrogen-rich compounds can become metallic and superconducting at lower pressures than hydrogen. More specifically, he proposed a novel way to pre-compress hydrogen chemically by examining IVa hydrides.[
]
In 2016, research suggested a link between the palladium hydride containing small impurities of sulfur nanoparticle
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
s as a plausible explanation for the anomalous transient resistance drops seen during some experiments, and hydrogen absorption by cuprates was suggested in light of the 2015 results in 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. It is also possible that if the bipolaron explanation is correct, a normally semiconducting material can transition under some conditions into a superconductor if a critical level of alternating spin coupling in a single plane within the lattice is exceeded; this may have been documented in very early experiments from 1986. The best analogy here would be anisotropic magnetoresistance
Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bul ...
, but in this case the outcome is a drop to zero rather than a decrease within a very narrow temperature range for the compounds tested similar to " re-entrant superconductivity".
In 2018, support was found for electrons having anomalous 3/2 spin states in YPtBi. Though YPtBi is a relatively low temperature superconductor, this does suggest another approach to creating superconductors.
It was also discovered that many superconductors, including the cuprates and iron pnictides, have two or more competing mechanisms fighting for dominance ( Charge density wave) and excitonic states so, as with organic light emitting diodes and other quantum systems, adding the right spin catalyst may by itself increase ''T''c. A possible candidate would be iridium
Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...
or gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile ...
placed in some of the adjacent molecules or as a thin surface layer so the correct mechanism then propagates throughout the entire lattice similar to a phase transition. As yet, this is speculative; some efforts have been made, notably adding lead
Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...
to BSCCO, which is well known to help promote high ''T''c phases by chemistry alone. However, relativistic effects similar to those found in lead-acid batteries might be responsible suggesting that a similar mechanism in mercury- or thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes a ...
-based cuprates may be possible using a related metal such as tin.
Any such catalyst would need to be nonreactive chemically but have properties that affect one mechanism but not the others, and also not interfere with subsequent annealing and oxygenation steps nor change the lattice resonances excessively. A possible workaround for the issues discussed would be to use strong electrostatic fields to hold the molecules in place during one of the steps until the lattice is formed.
Some research efforts are currently moving towards ternary
Ternary (from Latin ''ternarius'') or trinary is an adjective meaning "composed of three items". It can refer to:
Mathematics and logic
* Ternary numeral system, a base-3 counting system
** Balanced ternary, a positional numeral system, usef ...
superhydrides
A polyhydride or superhydride is a compound that contains an abnormally large amount of hydrogen. This can be described as high hydrogen stoichiometry. Examples include iron pentahydride FeH5, LiH6, and LiH7. By contrast, the more well known lit ...
, where it has been predicted that ( bilithium magnesium hexadecahydride) would have a of at 250 GPa (much hotter than what is normally considered room temperature).
See also
*
References
{{Reflist
Superconductors
Hypothetical technology
High pressure science