Metallic Hydrogen: A Liquid Superconductor?
Metallic Hydrogen: A Liquid Superconductor? Craig M. Tenney, Zachary F. Croft, and Jeffrey M. McMahon Department of Physics and Astronomy, Washington State University ∗
Introduction
Liquid Structure
Superconductivity
Background
In an ordinary liquid, atoms do not show any form of long-range order.
The prior features result in high-temperature superconductivity:
In 1935, Wigner and Huntington predicted1 that high pressures would dissociate molecular hydrogen into an atomic, metallic phase.
Qualitatively, this is seen in liquid metallic hydrogen:
support these arguments.
Motivation Determining whether liquid metallic hydrogen is a high-temperature superconductor is important for several reasons: • Fundamental physics: There is no known liquid superconductor. Such would constitute a new state of matter. • Planetary physics: Gas giants (planets) are comprised primarily of liquid metallic hydrogen. • Applications: High- and room-temperature superconductors would have significant applications in energy, electronics, etc.
310 300
https://labs.wsu.edu/mcmahon/
500
600
700
800
900
Figure: Superconducting critical temperatures Tc .
Figure: Snapshots from dynamical simulations, at 550 GPa and 500 K.
Quantitative measures, however, show anomalous local structure: 1.75 300 K 500 K 700 K 900 K
300 K 500 K 700 K 900 K
2.0
1.5
g(r)
S(q)
1.05
Concluding Remarks
0.70
1.0
0.35
0.5
0.00 0.0
Note: These temperatures are above those calculated5 for melting.
2.5
0.5
1.0
2.0
1.5
2.5
0.0
3.0
0
2
4
8
6
10
12
-1
r (Å)
q (Å )
Figure: Structural measures, at 500 GPa.
Phonons Phonon spectra calculated from dynamical simulations are similar to those from (static) snapshots:
Summary • Liquid metallic hydrogen is a high-temperature superconductor • ... (above the melting temperature5). Future work • Determine and analyze the uncertainties in the calculations.
0.04 dynamic 1 2 3
0.03
Acknowledgments
0.02
Startup support:
0.01
0 0
1000
2000
ω
3000
4000
(cm-1)
Figure: Phonon density of states F (ω).
Department of Physics and Astronomy
The bare Coulomb attraction results in large electron–phonon coupling: 1.2
1 2 3
1.0
References
0.8
0.6
2
1. Simulate liquid metallic hydrogen. 2. Calculate phonons (spectrum). 3. Calculate electron–phonon coupling. 4. Calculate superconducting critical temperature.
400
Pressure (GPa)
α F(ω)
General approach
340
320
Electron–Phonon Coupling Methods
350
330
F(ω) / proton
Recent calculations
4,5
500 K 1000 K
360
1.40
Such arguments further suggest3 that metallic hydrogen may be superconducting even in the liquid phase: • The superconducting critical temperature (in the solid) is expected to be greater than the melting temperature. • The phonon spectrum should be similar in both the solid and liquid phases. • Disorder doesn’t inhibit superconductivity.
370
Tc (K)
Theoretical arguments suggest2 that (solid) metallic hydrogen should be a high-temperature superconductor: • The ions in the system are protons; their small mass should cause the vibrational energy scale of the phonons to be high. • The electron–ion interaction is due to the bare Coulomb attraction; the electron–phonon coupling should thus be strong. • The electronic density of states at the Fermi surface should be large; and the Coulomb repulsion between electrons low.
380
0.4
0.2
0 0
1000
2000
ω
3000
4000
(cm-1)
Figure: Electron–phonon spectral function α2F (ω).
1. E. Wigner and H. B. Huntington, J. Chem. Phys. 3, 764 (1935) 2. N. W. Ashcroft, Phys. Rev. Lett. 21, 1748 (1968) 3. J. E. Jaffe and N. W. Ashcroft, Phys. Rev. B 23, 6176 (1981) 4. J. M. McMahon and D. M. Ceperley, Phys. Rev. B 84, 144515 (2011) 5. J. M. McMahon et al., Submitted (2017)
∗
[email protected]
Introduction
Liquid Structure
Superconductivity
Background
In an ordinary liquid, atoms do not show any form of long-range order.
The prior features result in high-temperature superconductivity:
In 1935, Wigner and Huntington predicted1 that high pressures would dissociate molecular hydrogen into an atomic, metallic phase.
Qualitatively, this is seen in liquid metallic hydrogen:
support these arguments.
Motivation Determining whether liquid metallic hydrogen is a high-temperature superconductor is important for several reasons: • Fundamental physics: There is no known liquid superconductor. Such would constitute a new state of matter. • Planetary physics: Gas giants (planets) are comprised primarily of liquid metallic hydrogen. • Applications: High- and room-temperature superconductors would have significant applications in energy, electronics, etc.
310 300
https://labs.wsu.edu/mcmahon/
500
600
700
800
900
Figure: Superconducting critical temperatures Tc .
Figure: Snapshots from dynamical simulations, at 550 GPa and 500 K.
Quantitative measures, however, show anomalous local structure: 1.75 300 K 500 K 700 K 900 K
300 K 500 K 700 K 900 K
2.0
1.5
g(r)
S(q)
1.05
Concluding Remarks
0.70
1.0
0.35
0.5
0.00 0.0
Note: These temperatures are above those calculated5 for melting.
2.5
0.5
1.0
2.0
1.5
2.5
0.0
3.0
0
2
4
8
6
10
12
-1
r (Å)
q (Å )
Figure: Structural measures, at 500 GPa.
Phonons Phonon spectra calculated from dynamical simulations are similar to those from (static) snapshots:
Summary • Liquid metallic hydrogen is a high-temperature superconductor • ... (above the melting temperature5). Future work • Determine and analyze the uncertainties in the calculations.
0.04 dynamic 1 2 3
0.03
Acknowledgments
0.02
Startup support:
0.01
0 0
1000
2000
ω
3000
4000
(cm-1)
Figure: Phonon density of states F (ω).
Department of Physics and Astronomy
The bare Coulomb attraction results in large electron–phonon coupling: 1.2
1 2 3
1.0
References
0.8
0.6
2
1. Simulate liquid metallic hydrogen. 2. Calculate phonons (spectrum). 3. Calculate electron–phonon coupling. 4. Calculate superconducting critical temperature.
400
Pressure (GPa)
α F(ω)
General approach
340
320
Electron–Phonon Coupling Methods
350
330
F(ω) / proton
Recent calculations
4,5
500 K 1000 K
360
1.40
Such arguments further suggest3 that metallic hydrogen may be superconducting even in the liquid phase: • The superconducting critical temperature (in the solid) is expected to be greater than the melting temperature. • The phonon spectrum should be similar in both the solid and liquid phases. • Disorder doesn’t inhibit superconductivity.
370
Tc (K)
Theoretical arguments suggest2 that (solid) metallic hydrogen should be a high-temperature superconductor: • The ions in the system are protons; their small mass should cause the vibrational energy scale of the phonons to be high. • The electron–ion interaction is due to the bare Coulomb attraction; the electron–phonon coupling should thus be strong. • The electronic density of states at the Fermi surface should be large; and the Coulomb repulsion between electrons low.
380
0.4
0.2
0 0
1000
2000
ω
3000
4000
(cm-1)
Figure: Electron–phonon spectral function α2F (ω).
1. E. Wigner and H. B. Huntington, J. Chem. Phys. 3, 764 (1935) 2. N. W. Ashcroft, Phys. Rev. Lett. 21, 1748 (1968) 3. J. E. Jaffe and N. W. Ashcroft, Phys. Rev. B 23, 6176 (1981) 4. J. M. McMahon and D. M. Ceperley, Phys. Rev. B 84, 144515 (2011) 5. J. M. McMahon et al., Submitted (2017)
∗
[email protected]
