The Wigner‐Huntington Transition to Metallic Hydrogen and ... · density and this overlaps the...
Transcript of The Wigner‐Huntington Transition to Metallic Hydrogen and ... · density and this overlaps the...
The Wigner‐Huntington Transition to Metallic Hydrogen
andLiquid MH: Isotope Effects
Isaac F. SilveraLyman Laboratory of Physics,
Harvard University
Support from the SSAA program
UG research
Kaan Yay
Hanl Park
Rachel Husband postdocSoon to DESY/PETRA Lab, Germany
Mohamed Zaghoo former gradNow at Laser Energetics Lab Rochester
Ranga Dias former postdocNow at Dept. of PhysicsUniv. of Rochester
Ori Noked former postdocHere at Harvard and medical entrepreneur
Subramanian NatarajanSenior res. Associate, Harvard.
Daniel Fernandez
Ashkan Salamatformer PD now on physics faculty at UNLV
Former Students now at the National Labs or SSAA support
Hector Lorenzana LivermoreJon Eggert LivermoreWill Evans Livermore
Todd Ditmire TexasMohamed Zaghoo Laser Energetics‐Omega
Former Postdocs Training the next generation High Density researchShanti Deemyad U. of UtahAshkan Salamat UNLVRanga Dias U. of Rochester
A single hydrogen moleculeis almost spherical
Binding energy4.74eV= 55,000 K
ZPE of the molecular vibration
Dissociation energy=Binding E‐(Zero‐Point E)4.47 eV=51,960 K
Deuterium with a larger mass and smaller ZPE has
Dissoc E: 4.556eV=52,870K
I.F. Silvera, "The Solid Molecular Hydrogens in the Condensed Phase: Fundamentals and Static Properties,Rev. Mod. Physics, vol. 52, pp. 393‐452, 1980.
Wigner‐Huntington 1935
High pressure hydrogen transforms to an atomic metal
Neil Ashcroft 1968
Atomic metallic hydrogen: a high temperature SC.
We pressurize and study hydrogen in a Diamond Anvil Cell (DAC)
at low temperatures
Density: 1 11‐12? ~14?
Pressure 0 300‐400 GPa? 400‐600 GPa?
High Tcsuperconductivity
Liquid?High Tc Supercond.Metastable Metal?
~3.8Å
~0.74Å
molecular solidInsulator, P=0
Metallic Hydrogen: Theory, Predictions
• Insulator-Metal Transition in Solid Hydrogen-- 25 GPa=0.25 megabarWigner, Huntington, 1935
• High Temperature Superconductivity in Atomic Metallic HydrogenAshcroft , 1968
• Molecular Metal at high pressureHarris, Monkhorst, 1971—also predicted to be high Tc superconductor
• Metastability, liquid at T=0 K and ambient pressureBrovman, Kagan, Kholas, 1972 1 eV barrier between molecular and metallic phases
• Later: Temperature driven dissociation at high temperature to liquid metallic hydrogen: the Plasma Phase Transition (PPT)
________________________________________________________• Modern calculations of the critical pressure for metallization– 4-5 megabar• Room temperature superconductor?• Is MH metastable?• Powerful Rocket Fuel: Isp (specific impulse) 1700 s. Cole, Silvera, Foote 2008
Historic
Modern
A remarkable change in the Phase Diagram of Hydrogendeveloped in the last decades
There are Two Pathways to Metallic Hydrogen
shown in the next viewgraph.
Metallic hydrogen might be a liquid or a solid in the HP low T region
I‐V:Structural transitions in the molecular phase
Culet flat
Double beveledculet flat
16 FACETED DIAMOND ANVILS
Laser Illumination
Scattered light
3-4 mm diameter at the girdle
30-100 micron diameter at the culet
A few recent Theoretical Predictions: Due to the large zero‐point energy of hydrogen Density Functional Theory (DFT) is inadequate
Path‐Integral, Quantum Monte‐Carlo: better predictions.
Some references (incomplete list!):
E. Wigner and H. B. Huntington, "On the Possibility of a Metallic Modification of Hydrogen," J. Chem. Phys., vol. 3, pp. 764‐770, 1935.
C. J. Pickard, M. Martinez‐Canales, and R. J. Needs, "Density functional theory study of phase IV of solid hydrogen," Phys. Rev. B, vol. 85, pp. 214114‐8, 2012.
H. Liu, and Y. Ma, Phys. Rev. Lett. 110, 025903 (2013). Proton or deuteron transfer in Phase IV of solid hydrogen and deuterium.
J. M. McMahon, M. A. Morales, C. Pierleoni, and D. M. Ceperley, "The properties of hydrogen and helium under extreme conditions," RevModPhys, vol. 84, no. 4, pp. 1607‐1653, 2012.
J. McMinis, R. C. C. III, D. Lee, and M. A. Morales, "Molecular to Atomic Phase Transition in Hydrogen under High Pressure," Phys. Rev. Lett., vol. 114, p. 105305, 2015.C. J. Pickard, M. Martinez‐Canales, and R. J. Needs, "Density functional theory study of phase IV of solid hydrogen," Phys. Rev. B, vol. 85, pp. 214114‐8, 2012.
C. Pierleoni, M. A. Morales, G. Rillo, M. A. Strzhemechny, M. Holzmann, and D. M. Ceperley, "Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations," PNAS, vol. 113, no. 18, pp. 4953‐4957, 2016.
S. Azadi, B. Monserrat, W. M. C. Foulkes, and R. J. Needs, "Dissociation of High‐Pressure Solid Molecular Hydrogen: A Quantum Monte Carlo and Anharmonic Vibrational Study," Phys. Rev. Lett., vol. 112, p. 165501(5), 2014.
N. D. Drummond, B. Monserrat, J. H. Lloyd‐Williams, P. L. Rios, C. J. Pickard, and R. J. Needs, "Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures," Nature Comm., vol. 6, p. 7794, 2015.
J. Chen et al., "Quantum simulation of low‐temperature metallic liquid hydrogen," Nature Comm., vol. 4, p. 2064, 2013.
H.Geng, R. Hoffman, and Q.Wu “Lattice stability and high‐pressure melting mechanism of dense hydrogen up to 1.5 TPa, Phys. Rev B92,104103, 2015
Predicted Solid (space group space group I41/amd) or Liquid ground state
What has prevented the observation of the Wigner‐Huntington transition to
atomic metallic hydrogen?
It’s the diamonds! They break before the required pressure is achieved.
In the past several years reported pressures on hydrogen and its isotopes was steadily increasing to ˜3.5 megabar.
Several months ago we achieved 4.2 megabar, and finally ˜ 5 megabar to make MH.
How did we do it?
• We used synthetic diamonds (CVD grown)naturals tend to be inhomogeneous and have inclusions.
• Removed microscopic surface damage using Reactive Ion Etching and annealing to remove residual stress in the diamonds
• Precision alignment so that the diamond culets remain opposed and parallel to the highest loads.
• Diamonds coated with alumina (Al2O3) that acts as a diffusion barrier against hydrogen into the diamonds. Inhibits diffusion and embrittlement.
• Maintain the hydrogen and diamonds at liquid nitrogen temperature (˜77K). Cryogenic loading. Inhibits diffusion.
• Never Shine significant laser power into the highly stressed diamonds. Known to cause diamond failure.
Run I‐‐Hydrogen: max. pressure 420 GPaObserved using IR spectrocopy
420 GPa
Dias, Noked, Silvera, FTIR spectra find a new phase line: arXiv:1603.02162v1
Low T pathway
Transparent black opaque shiny metalNext Run
205 GPa 415 GPa 495 GPa
Pictures taken with an iphone camera at the ocular of a stereo microscope
Reflectance and fit to the Drude free‐electron model
No correction for diamond absorption.
Originally we fit the 4 reflectances (404, 732, 642.6, and 1555 nm), but due to uncertainty in diamond absorption in the blue we have thrown out the first two points.(erratum Science, Vol. 355 Aug.18,2017)
Fit of reflectance to red and IR line (using Drude Model) where diamond absorption is unimportant.
From the Drude fit the plasma frequency yields the charge carrier density and this overlaps the atom density: atomic metallic hydrogen
H2‐PRE
Pathway II to liquid metallic hydrogen
Technique: pressurize to 100‐200 GPa then heat with pulsed laser
Heart of the DAC with semi‐transparent thin film of tungsten that acts as a laser absorber:
Alumina coating acts as a diffusion barrier
Pulsed laser for heating of W film
PeakTemperature
A kink or plateau in a heating curvecan signal a phase transition
Average pulse power
kink
plateau
Increased pulse energy goes into latent heat, not raising T.
Transmission and Reflection on the plateau or at higher temperatures than the plateau when the
liquid metallic hydrogen film is thin
Heating laser pulse
H2‐PRE
Pathway II to liquid metallic hydrogen
Technique: pressurize to 100‐200 GPa then heat with pulsed laser
We have now studied the PPT in Deuterium, using static pressure in a DACWe measure both pressure and temperature!
At high pressure the molar densities of hydrogen and deuterium are the same at a given pressure, ie the HP EOS is the same (experiment)
At the same pressure (molar density) we find an isotope effect of ~700 K.
Hydrogen
Deuterium
Deuterium at the Z‐Machine
CEIMC calculations (Ceperley collaboration: Pierleoni et al)find an isotope shift of ~200 K.
Interesting fact:The dissociation energy of free molecules of hydrogen and deuterium differ ~900 K
Binding energy is ~55,000 K
Difference in dissociation energy is due to the different zero‐point energies of the vibrational ground state.
Where can liquid metallic hydrogen be found? Jupiter is mostly hydrogen and a bit of helium.
The core, possibly molten, is surrounded by liquid metallic hydrogen. This is responsible for the magnetic field, via a dynamo effect.
Estimates at the core: Pressure 30‐45 megabars; Temperature ˜36,000 K
Future Plans
• Repeat the experiment• X‐ray determination of ground state structure: liquid or solid• Measure conductivity vs T: superconductivity• Show if it is metastable• Produce MH at lower pressures
Creation of the Wigner‐Huntington MH in our laboratory: probably the first occurrence of MH in
the Universe (the low temperature phase)