title: Electronic excitations and metallization of dense solid hydrogen.
abstract: Theoretical calculations and an assessment of recent experimental results for dense solid hydrogen lead to a unique scenario for the metallization of hydrogen under pressure. The existence of layered structures based on graphene sheets gives rise to an electronic structure related to unique features found in graphene that are well studied in the carbon phase. The honeycombed layered structure for hydrogen at high density, first predicted in molecular calculations, produces a complex optical response. The metallization of hydrogen is very different from that originally proposed via a phase transition to a close-packed monoatomic structure, and different from simple metallization recently used to interpret recent experimental data. These different mechanisms for metallization have very different experimental signatures. We show that the shift of the main visible absorption edge does not constrain the point of band gap closure, in contrast with recent claims. This conclusion is confirmed by measured optical spectra, including spectra obtained to low photon energies in the infrared region for phases III and IV of hydrogen.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA. rcohen@carnegiescience.edu
authors.forename: R E
authors.initials: RE
authors.lastname: Cohen
authors.forename: Ivan I
authors.initials: II
authors.lastname: Naumov
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley
mesh_terms: D004581:Electronics / Q000379:methods*; D006859:Hydrogen / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D011312:Pressure; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D008670:Metals; D006859:Hydrogen
keywords: density functional theory; diamond anvil cells; optical spectroscopy; semimetal absorption
references.citation: Phys Rev B Condens Matter. 1992 Sep 15;46(11):6688-6699
references.pmid: 10002369
references.citation: Phys Rev Lett. 1988 Aug 15;61(7):857-860
references.pmid: 10039448
references.citation: Proc Natl Acad Sci U S A. 2012 Jun 19;109(25):9766-9
references.pmid: 22665782
references.citation: Phys Rev Lett. 2012 Mar 23;108(12):125501
references.pmid: 22540596
references.citation: Phys Rev Lett. 2013 Jan 11;110(2):025903
references.pmid: 23383917
references.citation: Phys Rev Lett. 2011 Apr 22;106(16):165302
references.pmid: 21599379
references.citation: Phys Rev Lett. 1991 Aug 26;67(9):1138-1141
references.pmid: 10045085
references.citation: Phys Rev B Condens Matter. 1995 Sep 15;52(12):R8597-R8600
references.pmid: 9979903
references.citation: Phys Rev Lett. 1996 Mar 4;76(10):1667-1670
references.pmid: 10060487
references.citation: Nat Mater. 2011 Nov 13;10(12):927-31
references.pmid: 22081083
references.citation: Phys Rev Lett. 2013 May 24;110(21):217402
references.pmid: 23745931
references.citation: Phys Rev Lett. 1996 Mar 4;76(10):1663-1666
references.pmid: 10060486
references.citation: ACS Nano. 2011 Apr 26;5(4):2964-9
references.pmid: 21405129
references.citation: Phys Rev Lett. 2006 Jun 30;96(25):256802
references.pmid: 16907333
references.citation: J Chem Phys. 2012 Aug 21;137(7):074501
references.pmid: 22920125
references.citation: Phys Rev Lett. 2012 Apr 6;108(14):146402
references.pmid: 22540811