Faculty Profile

Ralph O Simmons

Ralph O Simmons
Ralph O Simmons

Primary Research Area

  • Condensed Matter Physics


  • PhD, Physics, University of Illinois, 1957
  • MA, Physics, Oxford University (UK), 1954
  • BA, Physics, Oxford University (UK), 1953
  • BA, Mathematics, University of Kansas, 1950


Following a postdoctoral appointment at Illinois, Ralph O. Simmons joined the physics faculty in 1959, teaching and establishing a research group studying properties of condensed gases (with support from the US Atomic Energy Commission). He was promoted to full professor in 1965, and became department head in 1970.

A formidable researcher, Simmons (with R. W. Balluffi) first proved that self-diffusion in the close-packed metals (Al, Cu, Ag, Au) proceeds by atomic vacancies. The "Simmons-Balluffi method" became a textbook example, notable as the direct and unambiguous way to determine the net vacancy content in crystals.

Simmons' interests then shifted to a neglected column of the periodic table--the noble gases--for which thermodynamic properties in the crystalline state had been limited to calorimetric and crude elastic studies. After techniques were perfected for growing and characterizing excellent crystals, a series of thermodynamic measurements on the whole family--Xe, Kr, Ar,Ne, and Ne isotopes--redefined, by two orders of magnitude, the precision with which such anharmonic properties as the thermal expansion are known. These studies provided data for critical tests of the theories of anharmonic lattice dynamics being developed in the 1960s.

His success in experimental physics has been grounded in development of new techniques in cryogenics and in imaginative x-ray instrument design. Going to higher pressures and lower temperatures, Simmons' group produced what remains the only direct x-ray measurements of equilibrium vacancy content of helium solids and unique x-ray structural studies of crystalline phase transformations in both solid helium and solid molecular hydrogen. No other laboratory has succeeded in carrying out similar x-ray work, despite considerable effort. Simmons' work may be pivotal in understanding the recently discovered "supersolid" phase of helium.

In the 1980s, Simmons pioneered the direct measurement of atomic momentum distributions in crystals of helium, neon, argon, molecular hydrogen, and other molecular solids, using pulsed neutron time-of-flight spectrometers. In the 1990s, his group used synchrotron x-rays to make the first quantitative studies of atomic vibration amplitudes in both crystal 3He and 4He. These neutron and x-ray scattering measurements have given definitive data for direct confrontation with the newest sophisticated computer simulations of quantum crystals. He also worked with several students to produce the first x-ray inelastic scattering studies of electronic excitations in solid and liquid helium and the first x-ray inelastic scattering measurements of phonon excitations in solid helium, especially the isotope 3He. Motivation for this work is elucidation of the dynamics, over extreme ranges of density and temperature, of the most extreme bulk 3D atomic quantum system known.

As department head, he recruited 43 faculty, including the now-Nobel laureate A. J. Leggett, and saw the completion of 514 PhD theses. His vision, leadership, and selection and mentoring of new faculty helped solidify the department's "Top 10" status, and #1 ranking in condensed matter physics. He also began the expansion of faculty in biomolecular physics, a significant part of current physics research at Illinois.

Simmons built strong ties with the Department of Astronomy, including joint faculty appointments, more astrophysical research, and the physical relocation of that department in proximity to physics. For a decade, he chaired a university committee to establish a Department of Atmospheric Sciences and oversaw its programs.

In 1986, Simmons returned to teaching and to his research as a member of the Frederick Seitz Materials Research Laboratory (of which he was a founding member). Altogether, he has supervised 33 doctoral dissertations at the University of Illinois and several other universities in Finland, the Netherlands, and Germany, and he was a pioneer in focusing national attention on the under-representation of women in U.S. physics.

Simmons also played an instrumental role in the development of a massive proposal to the National Science Foundation for a supercomputing center, which stimulated and eventually helped define a national policy for supercomputing centers and establishment of the National Center for Supercomputing Applications at Illinois.

In addition to numerous leadership and committee assignments at the University of Illinois, Simmons served a variety of science organizations, including the American Association for the Advancement of Science, American Institute of Physics, American Physical Society, and Institute of Physics (UK). He is a former chair of the Office of Physical Sciences for the US National Research Council. He chaired user and program committees at Argonne National Laboratory and Rutherford Appleton Laboratory (UK).

A Rhodes Scholar at Oxford, Simmons was elected a Fellow of the American Physical Society in 1962. He is a Fellow of the American Association for the Advancement of Science (1984), and a Senior University Scholar at Illinois. He received the Alexander von Humboldt Foundation Senior U.S. Scientist Award in 1992, and the University of Illinois College of Engineering's Distinguished Alumni Award in 2007.

Research Interests

  • Atomic motion in solids research in experimental condensed matter physics at UIUC


  • Distinguished Alumni Award, College of Engineering, University of Illinois (2007)
  • Alexander von Humboldt Foundation Senior US Scientist Award (1992)
  • Fellow, American Association for the Advancement of Science (1984)
  • Fellow, American Physical Society (1962)
  • Rhodes Scholar, Oxford University, UK (1950)