Silvera Group

Harvard University Department of Physics

 

Isaac F. Silvera

Thomas D. Cabot Professor of the Natural Sciences

 

Ph.D. 1965,

University of California, Berkeley

 

Group Home Page

[Prof. Silvera's Photograph]

 

Isaac Silvera's research is in both condensed matter and physics of cold particles. His interests are in ultra high pressure and low-temperature physics of quantum fluids.

 The high pressure physics uses diamond anvil cells to compress samples to pressures approaching 3 megabar. The current focus is on hydrogen and its isotopes, with an effort to produce and study metallic hydrogen, predicted to be a room temperature superconductor. The low pressure molecular hydrogen isotopes undergo a number of phase transitions as pressure is increased. New phases of orientational order called the broken symmetry phase and an as yet uncharacterized phase called the hydrogen-A phase above 1.5 megabar have been discovered. Techniques involve Raman scattering, IR spectroscopy, NMR, equation of state measurements, conductivity,  synchrotron x-ray studies, etc., as well as the development of high pressure methods and measurements. Recent developments are in the area of pulsed laser heating of samples.  Using short high power pulses at infrared wavelengths, samples can be heated to several thousand degrees K. Properties such as melting, metastable phases, etc, are studied under these extreme conditions of high pressure and temperature.

A new effort is underway is to stabilize and study multi-electron bubbles in helium.  These are spherical bubbles containing from 2 to of order 10^8 electrons and have diameters of tens of nanometers to hundreds of microns.  Due to Coulomb repulsion the electrons reside on the surface of the bubble in helium and form a two-dimensional gas.  Extremely high surface densities are predicted.  Current experiments are designed to visually observe the bubbles and measure some of their static properties.  At high enough density or low temperature the electron gas is expected to form a Wigner lattice, and at still higher densities the lattice is predicted to quantum melt due to increasing zero-point energy.  Bubbles have dynamic modes of oscillation (spherical riplons), high frequency plasma modes, etc.  Superconductivity has been predicted on a BCS model with electron-riplon coupling and is within access of experiment.

 

I. F. Silvera, "The solid molecular hydrogens in the condensed phase: fundamentals and static properties". Rev. Mod. Phys. 52: 393 (1980).

I. F. Silvera, "Metallic hydrogen," in The Metal-Insulator Transitions Revisited, ed. P. Edwards and C.N. Rao, (Taylor and Francis, London, 1995).

N. H. Chen, E. Sterer, and I. F. Silvera, "Extended infrared studies of high pressure hydrogen". Phys. Rev. Lett. 76: 1663 (1996).

L. Cui, N. H. Chen, and I. F. Silvera, "Excitations, order parameters, and phase diagram of solid deuterium at megabar pressures". Phys. Rev. B 51: 14987 (1995).

J. Tempere, I. F. Silvera, and J. T. Devreese, "The effect of pressure on  statics, dynamics and stability of multielectron bubbles," Phys. Rev. Lett., vol. 87, pp. 275301-277304, 2001.

I. F. Silvera, J. Tempere, J. Huang, and J. DeVreese, "Multi-electron bubbles under pressure," presented at Frontiers of High Pressure Research II: Application of High Pressure to Low Dimensional Novel Electronic Materials, 2001.

about
Led by Prof. Isaac F. Silvera, The Silvera Group is part of the Department of Physics at Harvard University. Some notable historic discoveries at high pressure include the discovery of megabar pressure phases in solid hydrogen and its isotopes, the metallization of xenon at megabar pressures, the metallization of hydrogen iodide, and highest pressures for NMR in a diamond anvil cell. In the study of low temperature quantum fluids, the stabilization and confinement of the first Bose gas, spin-polarized hydrogen, started the experimental search for Bose-Einstein condensation. Current research focuses on the metallization of solid hydrogen and the stabilization and trapping of multi-electron bubbles (MEBs) in superfluid helium.
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