Editing High-temperature superconductivity (section)

== Ongoing research ==
The question of how superconductivity arises in high-temperature superconductors is one of the major unsolved problems of theoretical [[condensed matter physics]]. The mechanism that causes the electrons in these crystals to form pairs is not known. Despite intensive research and many promising leads, an explanation has so far eluded scientists. One reason for this is that the materials in question are generally very complex, multi-layered crystals (for example, [[Bismuth strontium calcium copper oxide|BSCCO]]), making theoretical modelling difficult.

Improving the quality and variety of samples also gives rise to considerable research, both with the aim of improved characterisation of the physical properties of existing compounds, and synthesizing new materials, often with the hope of increasing {{mvar|T}}<sub>c</sub>. Technological research focuses on making HTS materials in sufficient quantities to make their use economically viable <ref>
{{cite journal
 |last1=Díez-Sierra |first1=Javier    |last2=López-Domínguez |first2=Pedro
 |last3=Rijckaert   |first3=Hannes    |last4=Rikel     |first4=Mark
 |last5=Hänisch     |first5=Jens     
 |display-authors=4
 |year=2021
 |title=All-chemical YBa2Cu3O7- $\delta$ coated conductors with preformed BaHfO3 and BaZrO3 nanocrystals on Ni5W technical substrate at the industrial scale
 |journal=Superconductor Science and Technology
 |volume=34 |issue=11 |pages=114001
 |doi=10.1088/1361-6668/ac2495
 |bibcode=2021SuScT..34k4001D |url=https://iopscience.iop.org/article/10.1088/1361-6668/ac2495/meta
|hdl=1854/LU-8719549
|s2cid=237591103 |hdl-access=free}}
</ref> as well as in optimizing their properties in relation to [[Technological applications of superconductivity|applications]].<ref>
{{cite journal
 |last1=Díez-Sierra |first1=Javier    |last2=López-Domínguez |first2=Pedro
 |last3=Rijckaert   |first3=Hannes    |last4=Rikel     |first4=Mark
 |last5=Hänisch     |first5=Jens      |last6=Khan      |first6=Mukarram Zaman
 |last7=Falter      |first7=Martina   |last8=Bennewitz |first8=Jan
 |last9=Huhtinen    |first9=Hannu     |last10=Schäfer  |first10=Sebastian
 |last11=Müller     |first11=Robert   |last12=Schunk   |first12=Stephan Andreas
 |last13=Paturi     |first13=Petriina |last14=Bäcker   |first14=Michael
 |last15=De Buysser |first15=Klaartje |last16=Van Driessche |first16=Isabel
 |display-authors=6
 |year=2020
 |title=High critical current density and enhanced pinning in superconducting films of YBa2Cu3O7−δ nanocomposites with embedded BaZrO3, BaHfO3, BaTiO3, and SrZrO3 nanocrystals
 |journal=ACS Applied Nano Materials
 |volume=3 |issue=6 |pages=5542–5553
 |doi=10.1021/acsanm.0c00814
 |url=https://pubs.acs.org/doi/pdf/10.1021/acsanm.0c00814
|hdl=1854/LU-8661998|s2cid=219429094 |hdl-access=free}}
</ref>
[[Metallic hydrogen]] has been proposed as a room-temperature superconductor, some experimental observations have detected the occurrence of the [[Meissner effect]].<ref>{{cite journal|first1=Jorge E.|last1=Hirsch|first2=Frank|last2=Marsiglio|title=Meissner effect in nonstandard superconductors|date=January 2021|journal=Physica C: Superconductivity and Its Applications|arxiv=2101.01701|doi=10.1016/j.physc.2021.1353896|issn=0921-4534|volume=587|bibcode=2021PhyC..58753896H |s2cid=230523758 }}</ref><ref>{{Cite journal|url=https://pubs.acs.org/doi/full/10.1021/acs.jpcc.1c05831|title=Metallic Hydrogen: A Liquid Superconductor?|first1=Craig M.|last1=Tenney|first2=Zachary F.|last2=Croft|first3=Jeffrey M.|last3=McMahon|date=18 October 2021|journal=The Journal of Physical Chemistry C|volume=125|issue=42|pages=23349–23355|doi=10.1021/acs.jpcc.1c05831|arxiv=2107.00098|s2cid=182128526}}</ref> [[LK-99]], [[copper]]-[[Doping (semiconductor)|doped]] lead-apatite, has also been proposed as a room-temperature superconductor.