Isaac Silvera

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Professor of physics

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Joel Halldorf

Stockholm School of Theology

Nicole Herbots

Arizona State University

PROF. OM PRAKASH SINHA

Amity University

Suseendran Jayachandran

IMEC

Ahmed A Abdala

Texas A&M University

Rafael Abargues

Universitat de València

Stephanie Seul

University of Bremen

Sergey Moiseev

Ulyanovsk State University

Nevra Akdemir

Universität Osnabrück

jean-michel guieu

Université Paris 1 - Panthéon-Sorbonne

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Papers by Isaac Silvera

Metallic hydrogen

Journal of Physics: Condensed Matter, May 31, 2018

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Reflectance of rhenium as a function of pressure in a diamond anvil cell

Applied Physics Letters

We have measured the reflectance of rhenium in the visible region to pressures up to 100 GPa in a... more We have measured the reflectance of rhenium in the visible region to pressures up to 100 GPa in a diamond anvil cell (DAC). By photographing the reflecting surface, we visually show that there are challenges to obtaining accurate values in a DAC for several reasons, including cupping of the diamonds and roughening of the surface with the increase in pressure. We propose some useful procedures, such as careful alignment of the incident light and using thin gaskets to minimize cupping of the diamonds as well as measurement in the central region of the diamond culet. We also show that knowledge of the reflectance of rhenium can overcome the problem of absorption of light by diamonds when studying the reflectance of materials at high pressure in a DAC.

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MAGNETIC PROPERTIES AND MAGNETIC STRUCTURES OF THE TCo$sub 3$ INTERMETALLIC COMPOUNDS, WHERE T IS A RARE EARTH METAL OR YTTRIUM

Infrared Absorption in Fe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>: Phenomenological Theory

Physical Review, Sep 16, 1966

A far-infrared absorption line has been observed in antiferromagnetic FeF2 at 154.4 cm '. The abs... more A far-infrared absorption line has been observed in antiferromagnetic FeF2 at 154.4 cm '. The absorption is greatest when the electric-field vector of the radiation is polarized parallel to the crystal c axis. The line broadens and shifts to lower frequencies as the temperature is raised, disappearing above the N(-. . 'el tempera- ture. The line strength is comparable to that of the antiferromagnetic resonance line observed at 53 cm The line does not disappear as T -+ 0, nor does it appear to broaden, shift, or split in a magnetic field. A theory based on a phenomenological spin Hamiltonian is presented which explains many of the properties of the line in terms of a two-magnon absorption process which predicts a line at 154 cm ' in excellent agreement with experiment. Another phenomenological theory of the same line by Moriya and the relationship of the present work to that of Al) en, Loudon, and Richards on MnF2 are discussed. The spin Hamiltonian used in this work is microscopically derived in the following paper.

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Novel Methods to Create Multielectron Bubbles in Superfluid Helium

arXiv (Cornell University), Oct 16, 2009

An equilibrium multielectron bubble in liquid helium is a fascinating object with a spherical two... more An equilibrium multielectron bubble in liquid helium is a fascinating object with a spherical two-dimensional electron gas on its surface. We describe two ways of creating them. MEBs have been observed in the dome of a cylindrical cell with an unexpectedly short lifetime; we show analytically why these MEBs can discharge by tunneling. Using a novel method, MEBs have been extracted from a vapor sheath around a hot filament in superfluid helium by applying electric fields up to 15 kV/cm, and photographed with high-speed video. Charges as high as 1.6x10 -9 C (~10 10 electrons) have been measured. The latter method provides a means of capture in an electromagnetic trap to allow the study of the extensive exciting properties of these elusive objects.

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1993 Ieee International Frequency Control Symposium Recent Investigations with the Harvard-Smithsonian Cryogenic Hydrogen Maser*

Step structure in the resistive transition of a type-II superconducting alloy

Physics Letters, May 1, 1968

Abstract For d.c. currents greater than a threshold value, the resistive superconducting-to-norma... more

Microwave trap for neutral atoms

OSA Annual Meeting

We demonstrated the microwave trap proposed for trapping atomic hydrogen by Agosta et al. [1].

Expanded Comment on: Optical Properties of Fluid Hydrogen at the Transition to a Conducting State

arXiv (Cornell University), Aug 16, 2016

In a recent paper McWilliams et al (MDMG) [1] measured transmittance, Tr, of high pressure-high t... more In a recent paper McWilliams et al (MDMG) [1] measured transmittance, Tr, of high pressure-high temperature hydrogen, heating to temperatures as high as 6000 K. They claim that hydrogen is a semiconductor or semi-metal at their conditions and there is no evidence of a firstorder phase transition to metallic hydrogen (MH). They laser heat an absorber embedded in hydrogen. The absorber has a central hole and they measure the transmittance through the hole. Their claim is based on a weak transmitted light signal interpreted as absorption in hydrogen that increases with increasing wavelength; they support this by a finite element analysis (FEA) and a nine-parameter fit to their data. They use a spatial filter to restrict the light that falls on the detector to that coming from the hole in the absorber. A spatial filter uses a lens to form a real magnified image of the sample in a focal plane; a small aperture in this plane is used to select the light from the absorber hole. The claim by MDMG is in contradiction with direct measurements of Tr and reflectance R of pressurized and heated dense hydrogen by Zaghoo, Salamat, and Silvera (ZSS) . ZSS provided strong evidence for an abrupt phase transition to a reflecting metallic phase of hydrogen when it is heated above a certain temperature identified as the phase transition temperature at the given pressure. They measured the Pressure-Temperature (P-T) phase line and optical reflectance of MH, R~0.5. Shock experiments on deuterium measured R ~0.5 . There is good agreement between the experimental phase line determined by ZSS and recent theory of Pierleoni et al . Twenty years ago Weir, Mitchel, and Nellis [7] measured metallic electrical conductivity of MH in a reverberating shock wave experiment, finding ~2000 S/cm. By contrast MDMG calculate DC conductivity of ~15 S/cm, two orders of magnitude smaller. There is no clear explanation for these differences from earlier work. This is a very challenging, complex experiment that relies heavily on interpretation. Their phase diagram is completely different from the one determined by ZSS. Hydrogen cannot have two different phase diagrams! Here we present an alternative model that can resolve the differences in the reported results. We first point to more problems or inconsistencies in the paper by MDMG. In contrast to their interpretation, they probably produced MH, but their resolution was inadequate to observe the transition as a plateau in T in a heating curve, as was done by ZSS and Ohta et al . MDMG pulse laser heat their sample with an approximately 5 µs long laser pulse having an unusual shape shown in Fig. . The pulse has an initial ~200 ns wide peak with ~3 times the power of the remaining 5 µs, and then slowly decays. The power is sufficient to heat to 5000-6000 K in the initial peak. The phase transition to MH can be identified by a plateau in a heating curve (a heating curve is a plot of sample temperature vs laser power or vs time). Temperatures rise rapidly in laser heated samples, so plateaus in heating curves are created at very short times. This has been shown experimentally by ZSS, and in a temperature/time curve studied with an FEA by Geballe and Jeanloz [9] (Fig. ). For the very large pulse power used by MDMG the temperature rises far above the plateau temperature observed by ZSS and would be a small "wrinkle" in the T vs. time curve (Fig. ). At MDMG's pressure of ~141 GPa, if MH was created,

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球表面上のCooperペアリングと超伝導液体ヘリウム中,多電子バブルに対するRichardson模型の適用

Physical Review B, 2005

Response to critiques on Observation of the Wigner-Huntington transition to metallic hydrogen

We reported the first observation of metallic hydrogen (MH) in the low temperature limit at a pre... more We reported the first observation of metallic hydrogen (MH) in the low temperature limit at a pressure of ~495 GPa in an article published in Science (1). This transition was first predicted by Wigner and Huntington (WE) over 80 years ago (2) at a pressure of ~25 GPa. In recent decades it became clear that the required pressure for metallization was far greater, in the 400-500 GPa range. Until now the observation of the WE transition in diamond anvil cells (DACs) has been prevented by one problem: the diamonds break before a sufficiently high pressure has been achieved. This has driven the high-pressure community to improve DACs and experimental methods to understand and overcome the conditions that limited the performance of diamonds and the pressure. In our experiment, with increasing pressure, we observed a clear transition from a transparent sample of solid molecular hydrogen to an opaque black sample to a shiny reflective sample of MH, as determined by reflectance measurements....

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The High-Pressure Search for Metallic Hydrogen

Inference: International Review of Science, 2022

In this energetic exchange, the original authors and Graeme Ackland express markedly differing vi... more

Rotational Temperatures and Densities in H2 and D2 Freejet Expansions

Rarefied Gas Dynamics, Parts I and II, 1981

Measurements relating to rotational relaxation infreejetexpansions of hL and D2 are reported. Dat... more Measurements relating to rotational relaxation infreejetexpansions of hL and D2 are reported. Data were obtained by means of Raman scattering. By this technique local rotational level populations were obtained in the range of 0.3 < x/D < 7 where x is the distance from the nozzle along the axis. Systematic measurements of the pressure dependence of the final rotational temperature in the jet are also described. Results show small deviations from an equilibrium Boltzmann distribution, with deviations (excesses) higher at the higher J levels. The present data are compared to a temperature relaxation model, and a new model that considers the evolution in the populations of the states in the jet. Radial and axial density profiles in the jet were also measured. The axial profile for H2 is found to correspond to a monatomic (y = 5/3) expansion.

Comment on: Observation of a first order phase transition to metal hydrogen near 425 GPa

arXiv: Other Condensed Matter, 2019

Loubeyre, Occelli, and Dumas (LOD) [1] claim to have produced metallic hydrogen (MH) at a pressur... more Loubeyre, Occelli, and Dumas (LOD) [1] claim to have produced metallic hydrogen (MH) at a pressure of 425 GPa, without the necessary supporting evidence of an insulator to metal transition. The paper is much ado about nothing. Most of the results have been reported earlier. Zha, Liu, and Hemley [2] studied hydrogen at low temperature up to 360 GPa in 2012; they reported absorption studies up to 0.1eV. Eremets et al [3] studied dense hydrogen up to 480 GPa using standard bevel diamonds. They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa. In 2016 Dias, Noked, and Silvera [4] reported hydrogen was opaque at 420 GPa. In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5].

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A Transition to Metallic Hydrogen: Evidence of the Plasma Phase Transition

Bulletin of the American Physical Society, 2015

Submitted for the MAR16 Meeting of The American Physical Society A Transition to Metallic Hydroge... more Submitted for the MAR16 Meeting of The American Physical Society A Transition to Metallic Hydrogen: Evidence of the Plasma Phase Transition1 ISAAC SILVERA, MOHAMED ZAGHOO, Lyman Laboratory of Physics, Harvard University, Cambridge,MA 02138, ASHKAN SALAMAT, Department of Physics, Univ. of Nevada at Las Vegas — The insulator-metal transition in hydrogen is one of the most outstanding problems in condensed matter physics. The high-pressure metallic phase is now predicted to be liquid atomic from T=0 K to very high temperatures. We have conducted measurements of optical properties of hot dense hydrogen in the region of 1.1-1.7 Mbar and up to 2200 K in a diamond anvil cell using pulsed laser heating of the sample. We present evidence in two forms: a plateau in the heating curves (average laser power vs temperature) characteristic of a first-order phase transition with latent heat, and changes in transmittance and reflectance characteristic of a metal for temperatures above the plateau te...

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New low temperature phase in dense hydrogen: The phase diagram to 421 GPa

arXiv: Other Condensed Matter, 2016

In the quest to make metallic hydrogen at low temperatures a rich number of new phases have been ... more In the quest to make metallic hydrogen at low temperatures a rich number of new phases have been found and the highest pressure ones have somewhat flat phase lines, around room temperature. We have studied hydrogen to static pressures of GPa in a diamond anvil cell and down to liquid helium temperatures, using infrared spectroscopy. We report a new phase at a pressure of GPa and T=5 K. Although we observe strong darkening of the sample in the visible, we have no evidence that this phase is metallic hydrogen.

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Metallic Hydrogen: A Game Changing Rocket Propellant

The objective of this research is to produce metallic hydrogen in the laboratory using an innovat... more The objective of this research is to produce metallic hydrogen in the laboratory using an innovative approach, and to study its metastability properties. Current theoretical and experimental considerations expect that extremely high pressures of order 4-6 megabar are required to transform molecular hydrogen to the metallic phase. When metallic hydrogen is produced in the laboratory it will be extremely important to determine if it is metastable at modest temperatures, i.e. remains metallic when the pressure is released. Then it could be used as the most powerful chemical rocket fuel that exists and revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system.

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No "Evidence for a new phase of dense hydrogen above 325 GPa

arXiv: Other Condensed Matter, 2016

In recent years there has been intense experimental activity to observe solid metallic hydrogen. ... more In recent years there has been intense experimental activity to observe solid metallic hydrogen. Wigner and Huntington predicted that under extreme pressures insulating molecular hydrogen would dissociate and transition to atomic metallic hydrogen. Recently Dalladay-Simpson, Howie, and Gregoryanz reported a phase transition to an insulating phase in molecular hydrogen at a pressure of 325 GPa and 300 K. Because of its scientific importance we have scrutinized their experimental evidence to determine if their claim is justified. Based on our analysis, we conclude that they have misinterpreted their data: there is no evidence for a phase transition at 325 GPa.

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Pressing Hydrogen into an Atomic Metallic Phase: Implications for Superconductivity

Bulletin of the American Physical Society, 2017

One of the great challenges to condensed matter physics is transforming solid molecular hydrogen ... more One of the great challenges to condensed matter physics is transforming solid molecular hydrogen to the atomic metallic phase predicted by Wigner and Huntington over 80 years ago. We have succeeded in producing metallic hydrogen in a diamond anvil cell at a pressure of 495 GPa. This is the highest pressure ever achieved on hydrogen and we shall discuss the measures taken to achieve this holy grail of high pressure physics. Metallic hydrogen was predicted to be a high temperature superconductor, years ago by Ashcroft; modern calculations predict the possibility of critical temperatures higher than room temperature. Recent high pressure experiments on hydrogen-rich hydrogen sulfide found a critical temperature above 200 K. The future will tell us if the pure substance, atomic metallic hydrogen, will finally achieve the goal of room temperature superconductivity.

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Quantum phase transition in solid hydrogen at high pressure

Physical Review B, 2019

Extensive experimental and theoretical studies have been devoted to determining the high-pressure... more Extensive experimental and theoretical studies have been devoted to determining the high-pressure phase diagram of hydrogen. We present evidence of a phase at a higher pressure than phase III and below the pressure of the recently observed phase of metallic hydrogen (495 GPa). This phase was determined from infrared (IR) spectroscopy of hydrogen samples at static pressures above 360 ± 15 GPa in a diamond anvil cell, and has been observed in three separate experiments. Whereas earlier studies found new high-pressure phases that only occurred at elevated temperatures, this phase transition occurs at the lowest temperatures investigated, ∼5 K, and the steep phase line indicates that it is a quantum phase transition. This phase is characterized by two distinct IR absorption bands (2950 and 3335 cm -1 at 365 GPa). Above the transition pressure we observe strong darkening of the sample in the visible spectrum as pressure is increased. Observations are compatible with the cmca-12 crystal structure.

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Metallic hydrogen

Journal of Physics: Condensed Matter, May 31, 2018

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Reflectance of rhenium as a function of pressure in a diamond anvil cell

Applied Physics Letters

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MAGNETIC PROPERTIES AND MAGNETIC STRUCTURES OF THE TCo$sub 3$ INTERMETALLIC COMPOUNDS, WHERE T IS A RARE EARTH METAL OR YTTRIUM