My main research interest since some time is dense and ultra-dense hydrogen forms. These materials are the lowest energy states of Rydberg Matter. This is a state of matter of the same status as liquid or solid, since it can be formed by a large number of atoms and small molecules. For a more complete description, see Wikipedia.
The lowest state of Rydberg Matter in excitation state n = 1 can only be formed from hydrogen (protium and deuterium) atoms and is designated H(1) or D(1). This is dense or metallic hydrogen, which we have studied for a few years. The bond distance is 153 pm, or 2.9 times the Bohr radius. It has a density of approximately 0.6 kg / dm3. See for example Ref. 167 below!
A much denser state exists for deuterium, named D(-1) or d(-1). We call it ultra-dense deuterium. This is the inverse of D(1), and the bond distance is very small, equal to 2.3 pm. Its density is extremely large, >130 kg / cm3. Due to the short bond distance, D-D fusion is expected to take place easily in this material. See Wikipedia! See also a press release and listen to a radio interview in Swedish (10.50 min into the program). A similar but not identical material formed from protium is called p(-1) or ultra-dense protium.
A theoretical description of ultra-dense deuterium D(-1) has been published by Friedwardt Winterberg. See these links to Journal of Fusion Energy, and Physics Letters A. The first experiments showing nuclear fusion in D(-1) can be found as Refs. 191 and 201 below.
Ultra-dense deuterium was recently shown to be the first room-temperature superfluid, see Ref. 196 below. It also shows a Meissner effect at room temperature (Ref. 204) and is thus probably also superconductive at room temperature.
Some recent publications:
210. P.U. Andersson and L. Holmlid, "Fast atoms and negative chain cluster fragments from laser-induced Coulomb explosions in a super-fluid film of ultra-dense deuterium D(-1)". Phys. Scripta, accepted.
207. F. Olofson, A. Ehn, J. Bood, L. Holmlid, "Large intensities of MeV particles and strong charge ejections from laser-induced fusion in ultra-dense deuterium".
206. F. Olofson and L. Holmlid, "Detection of MeV particles from ultra-dense protium p(-1): laser-initiated self-compression from p(1)".
205 L. Holmlid, "MeV particles from laser-initiated processes in ultra-dense deuterium D(-1)".
202. L. Holmlid, "Experimental studies of clusters of Rydberg matter and its extreme dense forms". Invited review.
200. L. Holmlid, "Sub-nanometer distances and cluster shapes in dense hydrogen and in higher levels of hydrogen Rydberg Matter by phase-delay spectroscopy".
199. L. Holmlid, "Diffuse interstellar bands (DIB) in space: almost all bands calculated from co-planar doubly excited He and metal atoms embedded in Rydberg Matter".
196. P.U. Andersson and L. Holmlid, "Superfluid ultra-dense deuterium D(-1) at room temperature".
194. P. U. Andersson, B. Lönn and L. Holmlid, "Efficient source for the production of ultra-dense deuterium D(-1) for laser-induced fusion (ICF)". Rev. Sci. Instrum. 82 (2011) 013503. doi:10.1063/1.3514985.
193. M. Trebala, W. Rozek, L. Holmlid, M. Molenda, and A. Kotarba,"Potassium stabilization in ß-K2Fe22O34 by Cr and Ce doping studied by field reversal method". Solid State Ionics (2011) . doi:10.1016/j.ssi.2010.08.004.
192. L. Holmlid, "Common forms of alkali metals - new Rydberg Matter clusters of potassium and hydrogen". J. Clust. Sci 21 (2010) 637-653. DOI: 10.1007/s10876-010-0291-0.
191. S. Badiei, P. U. Andersson and L. Holmlid, "Laser-driven nuclear fusion D+D in ultra-dense deuterium: MeV particles formed without ignition". Laser Part. Beams 28 (2010) 313-317 doi:10.1017/S0263034610000236.
190. P. U. Andersson and L. Holmlid, "Deuteron energy of 15 MK in a surface phase of ultra-dense deuterium without plasma formation: temperature of the interior of the Sun". Phys. Lett. A 374 (2010) 2856–2860
189. S. Badiei, P. U. Andersson and L. Holmlid, "Production of ultra-dense deuterium, a compact future fusion fuel". Appl. Phys. Lett. 96 (2010) 124103. doi:10.1063/1.3371718.
188. F. Olofson, P. U. Andersson and L. Holmlid, "Rydberg Matter clusters of alkali metal atoms: the link between meteoritic matter, polar mesosphere summer echoes (PMSE), sporadic sodium layers, polar mesospheric clouds (PMCs, NLCs), and ion chemistry in the mesosphere". arXiv.org 10-02-08, astro-ph/1002.1570. http://arxiv.org/abs/1002.1570
187. S. Badiei, P.U. Andersson and L. Holmlid, "Laser-induced variable pulse-power TOF-MS and neutral time-of-flight studies of ultra-dense deuterium". Phys. Scripta 81 (2010) 045601. doi: 10.1088/0031-8949/81/04/045601.
186. P. U. Andersson and L. Holmlid, "Ultra-dense deuterium: a possible nuclear fuel for inertial confinement fusion (ICF)". Phys. Letters A 373 (2009) 3067–3070. doi:10.1016/j.physleta.2009.06.046.
185. L. Holmlid, H. Hora, G. Miley and X. Yang, "Ultrahigh-density deuterium of Rydberg matter clusters for inertial confinement fusion targets". Laser and Particle Beams 27 (2009) 529–532.
183. S. Badiei, P. U. Andersson and L. Holmlid, "High-energy Coulomb explosions in ultra-dense deuterium: time-of-flight mass spectrometry with variable energy and flight length". Int. J. Mass Spectrom. 282 (2009) 70-76. Link to abstract and paper.
L. Holmlid, "Light in condensed matter in the upper atmosphere as the
origin of homochirality: circularly polarized light from Rydberg Matter". Astrobiol. 9 (2009)
179. S. Badiei, P. U. Andersson and L. Holmlid, "Fusion reactions in high-density hydrogen: a fast route to small-scale fusion?"
Int. J. Hydr. Energy 34 (2009) 487-495. Link to abstract and paper.
L. Holmlid, "Rydberg Matter - diary
from the laboratory" (translation of title in Swedish "Rydbergsmateria - dagbok från
labbet". Forskning och Framsteg 38:4 (2003) 14-17.