Dense quantum hydrogen
Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched metastably to a solid at ambient. The quantum nature of dense hydrogen is an iss...
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irk-123456789-1759542021-02-04T01:31:17Z Dense quantum hydrogen Nellis, W.J. Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched metastably to a solid at ambient. The quantum nature of dense hydrogen is an issue both at high pressures and in materials recovered metastably on release of pressure. Quantum zero point vibrations of H might have a significant affect on properties of metallic H at high pressures and might adversely affect lifetimes of metastable solid hydrogen, which is particularly relevant for applications. Metallic (degenerate) fluid H has been made at finite temperatures with a reverberating shock wave under dynamic compressions and under static compressions in laser-heated diamond-anvil cells. The pressure-temperature (P–T) regime in those experiments ranged up to 180 GPa and 3000 K, in which metallic fluid H is a quantum-degenerate fluid with T/TF << 1, where TF is Fermi temperature. The lifetime of an experiment under static compression near 500 GPa at 5.5 K ranged up to weeks, sufficiently long to warrant concern about quantum diffusion having a major affect on the chemical composition of that metallic sample. Ультраконденсований рідкий металевий водень отримано при високому тиску. Металевий водень мав би багато наукових та технологічних застосувань, якби міг залишатися в метастабільному стані при нормальних умовах. Питання про квантову природу щільного водню актуальне як при високому тиску, так і для матеріалів, які залишаються метастабільними при скиданні тиску. Квантові нульові коливання можуть істотно впливати на властивості металевого H при високому тиску і можуть несприятливо позначатися на часи життя метастабільного твердого водню, що особливо актуально для практичних застосувань. Металева (вироджена) рідина H була отримана при динамічному та статичному стисненні в умовах зворотної ударної хвилі в алмазній ковадлі, що нагрівається лазером.Тиск та температура в цих експериментах становили до 180 ГПа та 3000 К, при яких металева рідина Н являє собою квантово-вироджену рідину з Т/ТF << 1, де TF — температура Фермі. Час проведення експерименту при статичному стисненні близько 500 ГПа й температурі 5,5 К становив до декількох тижнів, що достатньо для спостереження квантової дифузії, яка має істотний вплив на хімічний склад цього металевого зразка. Ультраконденсированный жидкий металлический водород получен при высоких давлениях. Металлический водород имел бы много научных и технологических применений, если бы мог оставаться в метастабильном состоянии при нормальных условиях. Вопрос о квантовой природе плотного водорода актуален как при высоких давлениях, так и для материалов, которые остаются метастабильными при сбросе давления. Квантовые нулевые колебания могут существенно влиять на свойства металлического H при высоких давлениях и могут неблагоприятно сказываться на временах жизни метастабильного твердого водорода, что особенно актуально для практических применений. Металлическая (вырожденная) жидкость H получена при динамическом и статическом сжатиях в условиях возвратной ударной волны в нагреваемой лазером алмазной наковальне. Давление и температура в этих экспериментах составляли до 180 ГПа и 3000 К, при которых металлическая жидкость Н представляет собой квантово-вырожденную жидкость с Т/ТF << 1, где TF — температура Ферми. Время проведения эксперимента при статическом сжатии около 500 ГПа и температуре 5,5 К составляло до нескольких недель, что достаточно для наблюдения квантовой диффузии, имеющей существенное влияние на химический состав этого металлического образца. 2019 Article Dense quantum hydrogen / W.J. Nellis // Физика низких температур. — 2019. — Т. 45, № 3. — С. 338-34. — Бібліогр.: 16 назв. — англ. 0132-6414 http://dspace.nbuv.gov.ua/handle/123456789/175954 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
| topic |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) |
| spellingShingle |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) Nellis, W.J. Dense quantum hydrogen Физика низких температур |
| description |
Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several
scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched
metastably to a solid at ambient. The quantum nature of dense hydrogen is an issue both at high pressures and in
materials recovered metastably on release of pressure. Quantum zero point vibrations of H might have a significant affect on properties of metallic H at high pressures and might adversely affect lifetimes of metastable solid
hydrogen, which is particularly relevant for applications. Metallic (degenerate) fluid H has been made at finite
temperatures with a reverberating shock wave under dynamic compressions and under static compressions in laser-heated diamond-anvil cells. The pressure-temperature (P–T) regime in those experiments ranged up to
180 GPa and 3000 K, in which metallic fluid H is a quantum-degenerate fluid with T/TF << 1, where TF is Fermi
temperature. The lifetime of an experiment under static compression near 500 GPa at 5.5 K ranged up to weeks,
sufficiently long to warrant concern about quantum diffusion having a major affect on the chemical composition
of that metallic sample. |
| format |
Article |
| author |
Nellis, W.J. |
| author_facet |
Nellis, W.J. |
| author_sort |
Nellis, W.J. |
| title |
Dense quantum hydrogen |
| title_short |
Dense quantum hydrogen |
| title_full |
Dense quantum hydrogen |
| title_fullStr |
Dense quantum hydrogen |
| title_full_unstemmed |
Dense quantum hydrogen |
| title_sort |
dense quantum hydrogen |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2019 |
| topic_facet |
Спеціальний випуск. “Proceedings of 12th International Conference on Cryocrystals and Quantum Crystals (CC-2018)” (Wrocław, Poland, August 26–31, 2018) |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/175954 |
| citation_txt |
Dense quantum hydrogen / W.J. Nellis // Физика низких температур. — 2019. — Т. 45, № 3. — С. 338-34. — Бібліогр.: 16 назв. — англ. |
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Физика низких температур |
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AT nelliswj densequantumhydrogen |
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2025-07-15T13:33:53Z |
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| fulltext |
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3, pp. 338–341
Dense quantum hydrogen
W.J. Nellis
Department of Physics, Harvard University, Cambridge, MA 02138, USA
E-mail: nellis@fas.harvard.edu
Received October 24, 2018
Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several
scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched
metastably to a solid at ambient. The quantum nature of dense hydrogen is an issue both at high pressures and in
materials recovered metastably on release of pressure. Quantum zero point vibrations of H might have a signifi-
cant affect on properties of metallic H at high pressures and might adversely affect lifetimes of metastable solid
hydrogen, which is particularly relevant for applications. Metallic (degenerate) fluid H has been made at finite
temperatures with a reverberating shock wave under dynamic compressions and under static compressions in la-
ser-heated diamond-anvil cells. The pressure-temperature (P–T) regime in those experiments ranged up to
180 GPa and 3000 K, in which metallic fluid H is a quantum-degenerate fluid with T/TF << 1, where TF is Fermi
temperature. The lifetime of an experiment under static compression near 500 GPa at 5.5 K ranged up to weeks,
sufficiently long to warrant concern about quantum diffusion having a major affect on the chemical composition
of that metallic sample.
Keywords: ultracondensed metallic fluid, metallic hydrogen, high pressure.
1. Introduction
Ultracondensed metallic fluid H has been made at high
pressures by several groups. Solid metallic H would have
several scientific and technological applications if metallic
hydrogen made at high pressures could be quenched
metastably to a solid at ambient pressure. Toward that end,
experimental results and theoretical calculations about
metastability in general have been reviewed [1].
The quantum nature of dense hydrogenous materials is
an issue at high pressures and in materials recovered
metastably on release of high pressure. Quantum zero point
vibrations of H, for example, might adversely affect life-
times of metastable hydrogenous solids, which is particu-
larly relevant for technological applications. The purpose
of this paper is to assess the quantum nature of reported
cases of dense metallic H.
At density ρm = 0.62 mol H/cm3, “very low temperatures”
and some pressure P greater than 25 GPa (0.25·106 bar =
= 0.25 Mbar), Wigner and Huntington predicted that electri-
cally-insulating diatomic H2 would undergo an insulator–
metal transition (IMT) via molecular dissociation to mona-
tomic H [2]. Density ρm is 9-fold the density of H in liquid
H2 at 20 K. At that density the free-electron Fermi tempera-
ture of metallic H is TF = 220,000 K. Low finite temperatures
of a metal are those of a quantum-degenerate electron system
[3]. Thus, dense metallic H is expected to be quantum in na-
ture (T/TF << 1) for T of order a few 1000 K or less.
Dynamic compression [4] and static compression have
been used to achieve metallic H at high P. Dynamic com-
pressions have been generated by hypervelocity impact of
metal plates accelerated with a two-stage light-gas gun to
velocities as high as 8 km/s, with chemical explosives and
by intense optical irradiation from a pulsed laser. Lifetimes
of those dynamic experiments range between a few 100 ns
down to a few 10 ns.
Time at high pressures is an important consideration.
Dimensions of cylindrical specimens in dynamic experi-
ments are generally such that D/d ≈ 20, where D is diame-
ter and d is thickness. This shape and size maintain the
central volume of a specimen free from effects of pressure
release at sound speed from their edges. Lifetimes of dy-
namic compressions are sufficiently long to achieve ther-
mal equilibrium at high P in dense hydrogen and too brief
for undesirable effects to occur, such as thermal and mass
diffusion of H out of specimen volume during experi-
mental lifetime.
Lifetimes of static compressions in a diamond-anvil cell
(DAC) ranged from hours to days in laser-heated DACs.
An experimental lifetime in a DAC near 500 GPa at 5.5 K
ranged up to weeks, sufficiently long to warrant concern
about the occurrence of unexpected negative effects on the
© W.J. Nellis, 2019
Dense Quantum Hydrogen
specimen at late times. Historically, lifetimes of static
compressions are not constrained. Perhaps in some cases,
particularly for hydrogenous samples, experimental life-
times of static experiments would best be reported for rea-
sons discussed below.
2. Experimental results
Metallic fluid H (MFH) has been made under quasi-
isentropic dynamic compression at pressures P and tempera-
tures T achieved with reverberating shock waves [5–9]. Ex-
treme thermodynamic states were achieved mechanically by
conservation of mass, momentum and energy on each reflec-
tion of supersonic matter waves in H reflected off solid an-
vils. Electrical conductivities of dense fluid H were
measured with metal probes inserted through an Al2O3
anvil with measured negligible electrical conductivity.
Liquid-H2 specimens were initially 20 mm in diameter
and 0.5 mm thick [5,6]. The crossover from semi-
conductivity to poor metal [5,6] with Mott’s minimum
metallic conductivity (2000 (Ohm·cm)–1) [10] occurred
in experiments with 100 ns lifetimes. Reverberation com-
pleted at P = 140 GPa, T ≈ 3000 K, T/TF = 0.014 at den-
sity ρm predicted by Wigner and Huntington (WH) [2].
Those P/T are above the critical point Pc/Tc of the disso-
ciative phase transition. Thus, that crossover is continu-
ous from H2 to H with increasing P/T. Similar results
were measured in [7].
Using shock reverberation, electrical resistivities of fluid
silane (SiH4) have been measured up to 106 GPa [8]. Alt-
hough the metallization transition at 140 GPa could not be
confirmed because of the impact velocity limit and thus
shock-pressure limit (106 GPa) of their two-stage light-gas
gun, measured electrical resistivity of fluid silane drops
sharply with increasing pressure as reported previously for
fluid hydrogen [5–7]. This virtual coincidence in the semi-
conducting regime is attributed to decomposition of SiH4
into Si + 4 H with fluid H providing the major contribution
to electrical conductivity.
Quasi-isentropic compression of liquid D2 has been
achieved with shock reverberation generated at the Natio-
nal Ignition Facility (NIF) to increase P substantially slo-
wer than does a singe sharp shock-wave front. In a series
of such experiments at temperatures below 2000 K, a tran-
sition to metal-like reflectivity above 30% was observed in
fluid D near 200 GPa [9]. Metallization results in [9] and
[5,6] are in good agreement, given the different compres-
sive and diagnostic techniques employed.
Metallic states of hydrogen have also been made under
static compression in laser-heated DACs at high P and
finite T selectively along the dissociative phase transition
curve [11,12]. The diagnostic in those experiments was
energy of optical radiation incident on compressed H and
the relative amounts of optical reflection, absorption and
transmission. Pressures and temperatures achieved in the
fluid under dynamic (93–180 GPa/1700–3100 K) and static
(82–170 GPa/1100–2500 K) compressions are comparable,
although the trajectories in P–T space achieved under static
and dynamic compression differ because they were
achieved by different methods [4].
The above metallic fluids were made by both dynamic
and static compressions. Temperatures ranged between
1100 and 3000 K and pressures ranged between 82 and
140 GPa. At these high temperatures and associated high
densities metallic fluid H and D are quantum mechanically
degenerate (T/TF << 1). In this P–T regime, these metallic
fluids act as traditional metallic liquids.
3. DAC experiment at 5.5 K near 495 GPa
A single observation of metallic H has been reported
under static compression in a DAC at 5.5 K at an estimated
pressure of 495 GPa [13]. Optical reflectivity characteristic
of a metal was observed visually and measured in reflected
light. Obtaining such a high pressure in such a compressi-
ble sample in a DAC is a major accomplishment and an
interesting scientific result. However, although metallic
reflectivity was observed, there is a question as to the
chemical composition of the reflecting surface. The low
temperature of 5.5 K in 15-fold compressed H means that
quantum zero-point vibrations of dense H need to be con-
sidered in the analysis.
To prevent breaking diamonds in the DAC the com-
pression to 500 GPa was done slowly, on the time scale of
weeks, which process was successful. The key portion of
the sample consisted of a ~1 µm-thick layer of hydrogen
followed by an initially 50 nm-thick layer of alumina
(amorphous Al–O) deposited on the diamond flats of the
DAC. The alumina layer was assumed to be a “diffusion
barrier” of H into the diamond anvil. Reflectivity was as-
sumed to be from metallic H through the alumina, which
was assumed to be transparent at 500 GPa. Assuming
transparency of pure alumina is reasonable because the
calculated Hugoniot at high temperatures of Al2O3 does
not become metallic until 900 GPa [14]. Conventional non-
quantum diffusivity is a thermally-activated process. In
[13] H diffusion into alumina was assumed to be zero be-
cause of the low temperature of 5.5 K and the assumption
that H diffusion into alumina is thermally-activated.
However, dense H has intrinsic quantum zero-point vi-
brations (ZPV) at 5.5 K, which are not thermally activated.
ZPV represent jump attempts of H to diffuse into alumina.
Because of the high density of alumina at 500 GPa, the dif-
fusivity coefficient of H into alumina is expected to be
smaller than at ambient, whatever that value is, but neverthe-
less finite (non-zero) at high P. The weeks-long duration of
that experiment imply the possibility that after some of that
time a significant quantity of H might have diffused into the
alumina. Thus, even with a small diffusivity coefficient of H
into and through alumina, after a sufficiently long time it is
possible that an amorphous Al–O–H alloy formed and might
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3 339
W.J. Nellis
have become metallic with high reflectivity at 500 GPa, as
would many insulators at such a high pressure.
Thus, there are at least two possible explanations with
different reflecting surfaces as the source for the observed
reflecting metallic surface [13]. In one case, no H diffused
into alumina, which remained nonmetallic and transparent
up to ~500 GPa, near which pure H underwent a transition
to metallic H. In the other case, quantum ZPV generated a
sufficient number of H atoms that diffused through the
50 nm thick alumina to form an amorphous Al–O–H alloy
near 500 GPa, which became metallic with high reflectivity,
as would many insulators near 500 GPa. At present the only
thing known in this newly accessed regime of ultrahigh P
and cryogenic T is that a reflecting surface was formed near
500 GPa with a chemical composition that needs to be
determined.
At this point at least two experiments in a DAC at 5 K are
appropriate: (i) find a spectroscopic non-contact technique to
determine the chemical composition of the reflecting surface
near 500 GPa and (ii) measure the diffusion constant of H
atoms through various thicknesses of say 10–50 nm of alu-
mina at 500 GPa. Results in [13] indicate that at extremely
high densities and low temperatures it is possible to measure
properties of materials whose composition is unknown be-
cause of ZPV quantum effects in hydrogen. For this reason
documentation of the measured pressure, etc. histories and
diagnostic characterizations are useful for potential attempts
to reproduce such observations.
4. Dense quantum matter
The above analysis suggests that perhaps the most sci-
entifically interesting aspect implied by consideration of
15-fold compressed H at 5 K is the general issue of the
nature of dense quantum protium — the isotopes of hydro-
gen (H, D and T), which would include the question of
metallization of H. Study of protium offers the prospect of
checking mass-scaling relationships for quantum phenol-
mena in the lightest element. Interesting discoveries for H
and D might motivate research on T with its additional
issues of handling a radioactive material.
Such protium studies would involve both theory and
experiment. Important issues include (in no particular or-
der): (i) finding high-pressure protium phases, for example
as in [15], (ii) finding zero-point energies of dense
protium, (iii) learning how to quench novel hydrogenous
(and protium) phases made at high pressures to metastable
solids at ambient using methods implicit in [15], (iv) de-
termining whether the ground states of dense hydrogen
(and protium) is solid or fluid [16], and of course (v) de-
termining quantitatively thicknesses of diffusion barriers at
5 K calibrated versus pressure for H (and protium). The
latter point is a potential way to study the nature of quan-
tum zero-point vibrations themselves.
_______
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___________________________
Щільний квантовий водень
W.J. Nellis
Ультраконденсований рідкий металевий водень отримано
при високому тиску. Металевий водень мав би багато науко-
вих та технологічних застосувань, якби міг залишатися в мета-
стабільному стані при нормальних умовах. Питання про кван-
тову природу щільного водню актуальне як при високому
тиску, так і для матеріалів, які залишаються метастабільними
при скиданні тиску. Квантові нульові коливання можуть істот-
но впливати на властивості металевого H при високому тиску і
можуть несприятливо позначатися на часи життя метастабіль-
ного твердого водню, що особливо актуально для практичних
застосувань. Металева (вироджена) рідина H була отримана
при динамічному та статичному стисненні в умовах зворотної
ударної хвилі в алмазній ковадлі, що нагрівається лазером.
340 Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3
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https://doi.org/10.1126/science.aal1579
https://doi.org/10.1038/srep12823
https://doi.org/10.1063/1.3679751
https://doi.org/10.1063/1.3679751
Dense Quantum Hydrogen
Тиск та температура в цих експериментах становили до
180 ГПа та 3000 К, при яких металева рідина Н являє собою
квантово-вироджену рідину з Т/ТF << 1, де TF — температура
Фермі. Час проведення експерименту при статичному стис-
ненні близько 500 ГПа й температурі 5,5 К становив до декіль-
кох тижнів, що достатньо для спостереження квантової дифу-
зії, яка має істотний вплив на хімічний склад цього металевого
зразка.
Ключові слова: ультраконденсована металева рідина, мета-
левий водень, високий тиск.
Плотный квантовый водород
W.J. Nellis
Ультраконденсированный жидкий металлический водород
получен при высоких давлениях. Металлический водород
имел бы много научных и технологических применений, если
бы мог оставаться в метастабильном состоянии при нормаль-
ных условиях. Вопрос о квантовой природе плотного водорода
актуален как при высоких давлениях, так и для материалов,
которые остаются метастабильными при сбросе давления.
Квантовые нулевые колебания могут существенно влиять на
свойства металлического H при высоких давлениях и могут
неблагоприятно сказываться на временах жизни метастабиль-
ного твердого водорода, что особенно актуально для практи-
ческих применений. Металлическая (вырожденная) жидкость
H получена при динамическом и статическом сжатиях в усло-
виях возвратной ударной волны в нагреваемой лазером алмаз-
ной наковальне. Давление и температура в этих экспериментах
составляли до 180 ГПа и 3000 К, при которых металлическая
жидкость Н представляет собой квантово-вырожденную жид-
кость с Т/ТF << 1, где TF — температура Ферми. Время прове-
дения эксперимента при статическом сжатии около 500 ГПа и
температуре 5,5 К составляло до нескольких недель, что дос-
таточно для наблюдения квантовой диффузии, имеющей су-
щественное влияние на химический состав этого металличе-
ского образца.
Ключевые слова: ультраконденсированная металлическая
жидкость, металлический водород, высокое давление.
Low Temperature Physics/Fizika Nizkikh Temperatur, 2019, v. 45, No. 3 341
1. Introduction
2. Experimental results
3. DAC experiment at 5.5 K near 495 GPa
4. Dense quantum matter
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