Isaac F. Silvera
Thomas D. Cabot Professor of the Natural Sciences
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[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
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).
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.
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.