Isaac F. Silvera

The isotropic intermolecular potential for H2 and D2 in the solid and gas phases

A semiempirical pair potential for molecular hydrogen and deuterium has been derived by fitting to solid state data. The potential is bounded to conform asymptotically to short‐ and long‐range theoretical results. In the solid, many‐body effects are accounted for by including a spherical form of the nonnegligible Axilrod–Muto–Teller three‐body forces. The potential can be used to successfully describe isotropic properties in the solid and gas phases.

The ruby pressure standard to 150 GPa

A determination of the ruby high-pressure scale is presented using all available appropriate measurements including our own. Calibration data extend to 150 GPa. A careful consideration of shock-wav ...

Observation of the Wigner-Huntington transition to metallic hydrogen

Stamping hydrogen into metal In 1935, Wigner and Huntington predicted that molecular hydrogen would become an atomic metal at a pressure of 25 GPa. Eighty years and more than 400 GPa later, Dias and Silvera have finally produced metallic hydrogen at low temperature. The metallization occurred between 465 and nearly 500 GPa at 5.5 K. Spectroscopic measurements verified that hydrogen was in the atomic state. The observation completes an unexpectedly long quest to find the metallic hydrogen that Wigner and Huntington predicted so long ago. Science, this issue p. 715 Molecular hydrogen becomes an atomic metal between 465 and 495 gigapascals at low temperature. Producing metallic hydrogen has been a great challenge in condensed matter physics. Metallic hydrogen may be a room-temperature superconductor and metastable when the pressure is released and could have an important impact on energy and rocketry. We have studied solid molecular hydrogen under pressure at low temperatures. At a pressure of 495 gigapascals, hydrogen becomes metallic, with reflectivity as high as 0.91. We fit the reflectance using a Drude free-electron model to determine the plasma frequency of 32.5 ± 2.1 electron volts at a temperature of 5.5 kelvin, with a corresponding electron carrier density of 7.7 ± 1.1 × 1023 particles per cubic centimeter, which is consistent with theoretical estimates of the atomic density. The properties are those of an atomic metal. We have produced the Wigner-Huntington dissociative transition to atomic metallic hydrogen in the laboratory.

Melting line of hydrogen at high pressures.

The insulator to metal transition in solid hydrogen was predicted over 70 years ago but the demonstration of this transition remains a scientific challenge. In this regard, a peak in the temperature versus pressure melting line of hydrogen may be a possible precursor for metallization. However, previous measurements of the fusion curve of hydrogen have been limited in pressure and temperature by diffusion of hydrogen into the gasket or diamonds. To overcome this limitation we have used an innovative technique of pulsed laser heating of the sample and find a peak in the melting line at P=64.7+/-4 GPa and T=1055+/-20 K.

Diamond anvil cell and cryostat for low‐temperature optical studies

A diamond anvil cell and cryostat suitable for optical studies from 1.1 K to room temperature at ultrahigh pressures is described. Special provisions and techniques for loading condensable gases (cryogases) are discussed.

High-pressure equations of state of Al, Cu, Ta, and W

We have generated 300-K isotherms to pressures as high as 300 GPa for Al, Cu, Ta, and W. Hugoniot data were reduced to isotherms using calculated thermal pressures. For these four metals, available experimental results permitted corrections of Hugoniot data for shock-induced strength as a function of shock pressure. High-pressure shock-wave data are extended to zero pressure using ultrasonically determined bulk moduli. For ease of evaluation of pressure-volume points, the isotherms are presented in the Vinet [J. Phys. C 19, L467 (1986)] form of the equation of state, along with isotherms for Mo and Au and Pt.

Helium‐temperature beam source of atomic hydrogen

We describe a technique for producing a high‐flux beam of atomic hydrogen with a velocity distribution corresponding to liquid‐helium temperatures. We have studied how a gas of hydrogen atoms (H) may be cooled to low temperatures through interaction with cold walls. The gas was analyzed by forming an atomic beam. We obtained fluxes φH≃2.4×1016 atoms/s at T≃8 K, which corresponds to an increase in flux of low‐velocity atoms by a factor of 20 over that of the same source operated at room temperature. The degree of dissociation and the translational temperature of the gas were determined using a quadrupole mass spectrometer and time‐of‐flight techniques. A beam modulation technique advantageous for such a system is discussed and analyzed. General design considerations for the transport and cooling of H are presented and illustrated with examples. The methods of data analyses are discussed in detail.

Evidence of a liquid-liquid phase transition in hot dense hydrogen

We use pulsed-laser heating of hydrogen at static pressures in the megabar pressure region to search for the plasma phase transition to liquid atomic metallic hydrogen. We heat our samples substantially above the melting line and observe a plateau in a temperature vs. laser power curve that otherwise increases with power. This anomaly in the heating curve appears correlated with theoretical predictions for the plasma phase transition.

Chapter 3: Spin-Polarized Atomic Hydrogen

Publisher Summary This chapter reviews the properties of new quantum gases and properties of spin-polarized tritium. The hydrogen (H 2 ) atom with its single electron and proton, bearing a spinoff is the simplest and most abundant atom in the universe. The atomic species in a discharge is short lived and is recombined to form H 2 . The hydrogen maser, which operates on the zero-field hyperfine transitions of the hydrogen atom, has become the most stable time and frequency source in existence. The chapter discusses the properties of new quantum gases and some of the properties of spin-polarized tritium (Ti). These new quantum gases promise to have many new and exciting properties in the low-temperature, high-density regime of quantum degeneracy. The chapter also describes the theory of decay. Magnetic properties of the many-body gas concentrates on many-body phenomena on surfaces or in two-dimension. In the condensed state, hydrogen and its isotope deuterium provide physics with the two fundamental many-body quantum systems of nature, boson- and fermion-fluids. Because of its very light mass and weak interactions, a many-particle system of electron spin-polarized hydrogen is predicted to have the unique property that it will remain in the gaseous state at the absolute zero of temperature.

Improved adhesion of thin conformal organic films to metal surfaces

A technique is described for attaching thin, conformal, pin‐hole‐free electrically insulating polyethylene films to flat gold surfaces (previously modified by adsorption of a monolayer of an organic disulfide) by plasma polymerization. These polyethylene films are tough enough to support the attachment of gold electrodes.