The great magnetic resonance physicist, Charles Pence Slichter, passed away peacefully on Feb. 19, 2018, at the age of 94, in Boulder, Colorado. Charlie (as he liked to be called) was one of the early pioneers in the development of magnetic resonance methods, making numerous contributions to NMR, EPR, and NQR. He was President of ISMAR from 1987 to 1989, received the ISMAR prize in 1986, and became an ISMAR Fellow in 2008. Charlie was universally admired, not only for his scientific accomplishments, but also for his personal warmth, generosity, and positive outlook on life and science.
Charlie was born on Jan. 23, 1924 in Ithaca, NY. He received his Ph.D. in 1949 from Harvard University under the direction of Prof. Edward Purcell, then joined the faculty of the University of Illinois in Champaign-Urbana, where he remained for his entire career. He was promoted to Full Professor in 1955 (at the age of 31!). He formally retired in 1997, but continued other physics-related activities (e.g., attending colloquia, participating in group meetings of colleagues, reviewing papers, etc.) until his death.
Charlie’s service contributions, both national and international, were considerable. In addition to his service to ISMAR, he was a member of President Lyndon Johnson’s Science Advisory Committee (PSAC) from 1965 to 1969, a member of the Harvard Corporation from 1970 to 1995, and a member of the National Science Board from 1975 to 1984.
In addition to his honors from ISMAR, Charlie received many other honors during his illustrious career, including being an Alfred P. Sloan Fellow (1955-61), a member of the National Academy of Sciences (1967), a Fellow of the American Academy of Arts and Sciences (1969), a member of the American Philosophical Society (1971), and a Fellow of the American Physical Society (APS) (1955). He received the APS Langmuir Prize in Chemical Physics in 1969, the U.S. Department of Energy’s Division of Materials Science Award for Sustained Outstanding Research in Solid State Physics in 1984 and again in 1992, the Department of Energy's Award for Outstanding Scientific Accomplishment in 1993, the Comstock Prize of the National Academy of Sciences in 1993, and the APS Oliver E. Buckley Prize in Condensed Matter Physics in 1996. Charlie received the National Medal of Science from the U.S. President in 2007. He also received honorary doctoral degrees in Science from the Universities of Waterloo (1993) and Leipzig (2010) and an honorary doctorate in Law from Harvard (1996).
Charlie's research spanned many subfields of physics and chemistry and was characterized by elegant theoretical analyses and many, many beautiful experiments. His research not only answered fundamental questions in science but also resulted in the development of important techniques in magnetic resonance, many of which are widely used today. One of his most important early contributions to solid state physics was his measurements of the temperature dependence of spin-lattice relaxation in aluminum, which provided the first experimental support for the electron pairing concept of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity. In this landmark study, first reported only four months after the first paper by BCS in 1957, Charlie and his student Chuck Hebel observed an unanticipated peak in 1/T1 immediately below the superconducting transition temperature, arising from coherence factors unique to BCS. Slichter and Hebel then worked out the theory to explain this peak (now widely known as the "Hebel-Slichter peak") using the BCS wavefunction. In order to do this experiment, Slichter and Hebel first had to develop techniques for measuring NMR relaxation experiment in zero magnetic field. Their approach led to such methods as field cycling and adiabatic demagnetization in the rotating frame (ADRF).
Charlie and his students made important contributions to the development of double resonance techniques, including nuclear-nuclear double resonance and electron-nuclear double resonance (ENDOR). In a famous experiment, Charlie and his student Tom Carver provided the first experimental verification of Albert Overhauser’s prediction that saturation of the conduction electron resonance in a metal would lead to a 1000-fold increase in the polarization of the nuclear spins (the original "Overhauser effect"). When Charlie reported these results in a meeting of the APS, he was lambasted by a group of skeptical physicists, including several Nobel Prize winners who thought (incorrectly) that Overhauser’s ideas violated the second law of thermodynamics. (Erwin Hahn facetiously described this as a Nobel Prize grilling.) The Carver-Slichter experiment was the first demonstration of dynamic nuclear polarization (DNP), a phenomenon that continues to grow in importance to the present day.
Charlie’s contributions to chemistry were also significant. He was a co-discoverer (with Herb Gutowsky and Dave McCall) of indirect spin-spin (J) coupling in molecules. He also developed a theory of chemical shifts in which he explained the origin of the large 19F paramagnetic chemical shifts. In addition, Charlie provided the first detailed theory of the effect of rate processes on NMR spectra.
In 2017, the American Chemical Society recognized the discovery of J couplings at the University of Illinois with a Chemical Breakthrough Award. Charlie's own description of this discovery can be found at https://physics.illinois.edu/news/article/23848.
Other important achievements include the first absolute measurement of the electron spin susceptibility in metals, elucidation of the Kondo effect in solids by observation of nuclear quadrupolar satellites near magnetic atoms in dilute alloys, and observations of the motions of charge density waves in solids under applied electric fields. Charlie pioneered the use of rotating frame relaxation to extend by orders of magnitude the range over which translational diffusion and molecular motions could be observed in solids, developed spin temperature techniques for solving otherwise intractable problems such as calculating spin-lattice relaxation in zero applied field and in the ultraslow motion regime, and introduced phase-coherent detection of pulsed NMR (widely used in modern NMR equipment), thereby allowing the measurement of NMR signals that are much weaker than the noise.
Charlie's personal account of the history of superconductivity, including a recording in his own voice, is available at https://history.aip.org/history/exhibits/mod/superconductivity/01.html . Additional information about Charlie's life and times can be found at https://jfi.uchicago.edu/~leop/AboutPapers/Slichter-Bardeen.pdf and http://engineering.dev.engr.illinois.edu/news/article/24443 .
And then, of course, there is Charlie's influential textbook, “Principles of Magnetic Resonance”. The first edition of this book resulted from lectures that Charlie gave in the Spring of 1961 when he was a Morris Loeb Lecturer at Harvard. Subsequent editions greatly expanded the scope of the book to include more recent developments in multiple-pulse techniques, two-dimensional spectroscopy, magnetic resonance imaging, and multiple quantum NMR. One of the most significant characteristics of this book is Charlie’s method of describing different ways of looking at the same phenomenon as leading to an apparent contradiction, which he then proceeds to explain completely and clearly, thereby resolving the apparent contradiction. This fantastic book is still widely read by students of magnetic resonance and used as a basic reference by many of us, more than 50 years after its initial publication.
In addition to his outstanding research record, Charlie was one of the great physics teachers of our time. He supervised approximately 64 Ph.D. students and over 50 postdocs (including Sir Peter Mansfield, who received the Nobel Prize as a co-inventor of MRI). Many of these students and postdocs have gone on to leading positions in education and industry and have thus spawned even more great contributions.
Charlie had an interesting low-key approach to getting his students to work longer hours. He would show up in the lab at 8:00 AM for coffee and then disappear for the rest of the day. If we wanted to talk to him, we had to be in the lab by 8:00 AM. Charlie would always start conversations by saying “How did it go last night?”. Yes, we were expected to work long hours at night and still show up early in the morning.
Charlie had an amusing way of achieving privacy when necessary, even though he hated to say no to a student with questions. He acquired an additional nameplate with the name “Roger Willoughby” that he placed on the door to his office, covering his name. Whenever we saw that, we knew that he was not to be interrupted, yet solicitors and others would not know where to find him.
As many of his friends are aware, Charlie had a somewhat round head (or “moon-shaped” as he liked to say). We had in the lab a large and completely round 50 liter vessel on wheels for transporting liquid nitrogen between rooms. In order for us not to lose this vessel to another lab, we painted the letters “C.P.S.” on it. Charlie seemed to identify with this N2 vessel, since, whenever it was wheeled into his presence, he would break out into a broad grin.
Charlie’s interests in his former students and postdocs did not end with their leaving his labs. A “Slichter tradition” at each March Meeting of the APS for about 30 years was that all attending former Slichter students and postdocs and their students, etc. were invited to dinner, usually at a Chinese restaurant on a Tuesday night. Charlie’s sensitivities to the needs of students were illustrated by the requirement that all current students would be free and the rest of us would cheerfully chip in to cover their costs.
Charlie’s love for interactions with students is typified by a statement that he made at the 80th symposium held in his honor at the University of Illinois: “…If I were not in a research setting, I would have to find students to work with.”
Charles P. Slichter was greatly loved and will be sorely missed.
We thank Prof. David C. Ailion for preparing this obituary. David received his Ph.D. in physics from the University of Illinois for experiments in Charlie Slichter's lab in the mid-1960s, which demonstrated the use of rotating-frame NMR relaxation as a probe of ultra-slow atomic translational motions in solids. David also served as Treasurer of ISMAR from 2011 through 2017.