Editing Metallic hydrogen (section)

===Shock-wave compression, 1996===
In March 1996, a group of scientists at [[Lawrence Livermore National Laboratory]] reported that they had [[serendipity|serendipitously]] produced the first identifiably metallic hydrogen<ref>{{cite journal |last1=Weir |first1=S. T. |last2=Mitchell |first2=A. C. |last3=Nellis |first3=W. J. |year=1996 |title=Metallization of fluid molecular hydrogen at 140&nbsp;GPa (1.4&nbsp;Mbar) |journal=[[Physical Review Letters]] |volume=76 |issue=11 |pages=1860–1863 |bibcode=1996PhRvL..76.1860W |doi=10.1103/PhysRevLett.76.1860 |pmid=10060539 |quote=0.28–0.36&nbsp;mol/cm<sup>3</sup> and 2200–4400&nbsp;K}}</ref> for about a [[microsecond]] at [[temperature]]s of thousands of [[kelvin]]s, pressures of over {{convert|1000000|atm|GPa atm psi|order=out|abbr=on}}, and densities of approximately {{val|0.6|u=g/cm3}}.<ref name="Nellis">{{cite journal |last=Nellis |first=W. J. |year=2001 |title=Metastable Metallic Hydrogen Glass |url=https://e-reports-ext.llnl.gov/pdf/244531.pdf |journal=Lawrence Livermore Preprint UCRL-JC-142360 |osti=15005772 |osti-access=free |quote=minimum electrical conductivity of a metal at 140&nbsp;GPa, 0.6&nbsp;g/cm<sup>3</sup>, and 3000&nbsp;K |access-date=2018-02-24 |archive-url=https://web.archive.org/web/20161229095145/https://e-reports-ext.llnl.gov/pdf/244531.pdf |archive-date=2016-12-29 |url-status=dead }}</ref> The team did not expect to produce metallic hydrogen, as it was not using [[solid hydrogen]], thought to be necessary, and was working at temperatures above those specified by metallization theory. Previous studies in which solid hydrogen was compressed inside [[diamond anvil]]s to pressures of up to {{convert|2500000|atm|GPa atm psi|order=out|abbr=on}}, did not confirm detectable metallization. The team had sought simply to measure the less extreme [[Electrical resistivity and conductivity|electrical conductivity]] changes they expected. The researchers used a [[1960 in science|1960s-era]] [[light-gas gun]], originally employed in [[guided missile]] studies, to shoot an impactor plate into a sealed container containing a half-millimeter thick sample of [[liquid hydrogen]]. The liquid hydrogen was in contact with wires leading to a device measuring electrical resistance. The scientists found that, as pressure rose to {{convert|1400000|atm|GPa atm psi|order=out|abbr=on}}, the electronic energy [[band gap]], a measure of [[electrical resistance]], fell to almost zero. The band gap of hydrogen in its uncompressed state is about {{val|15|ul=eV}}, making it an [[electrical insulator|insulator]] but, as the pressure increases significantly, the band gap gradually fell to {{val|0.3|u=eV}}. Because the [[thermal energy]] of the fluid (the temperature became about {{convert|3000|K|C|disp=or|abbr=on}} due to compression of the sample) was above {{val|0.3|u=eV}}, the hydrogen might be considered metallic.