Charles Pence Slichter, a pioneer of magnetic resonance in the physical sciences, died peacefully on 19 February 2018 in Boulder, Colorado. Charlie will be remembered both for his tremendous contributions to science and for the warmth and optimism he conveyed to everyone fortunate enough to know him.

Charles Pence Slichter

Charlie was born on 21 January 1924 in Ithaca, New York. After working at the Underwater Explosives Research Laboratory at the Woods Hole Oceanographic Institution during World War II, he received his AB degree from Harvard University in 1947. Staying at Harvard, he earned his PhD in physics two years later under Edward Purcell for studies of electron spin resonance. Charlie then joined the physics department at the University of Illinois at Urbana-Champaign as an instructor. He was appointed assistant professor two years later, became a full professor in 1955, and remained at the university for the rest of his career.

Charlie’s research centered on NMR and spanned the fields of solid-state physics, materials science, and chemistry. In 1951, with his chemistry colleague Herbert Gutowsky and Gutowsky’s student David McCall, Charlie proposed the existence of scalar couplings between nuclear spins to explain splittings of NMR lines in spectra of molecular liquids. Scalar couplings became the basis for most subsequent studies of molecular structures by NMR, including modern multidimensional NMR of proteins and nucleic acids.

In 1953 Charlie and his student Thomas Carver performed the first experiments validating Albert Overhauser’s counterintuitive prediction that saturation of a metal’s electron spin resonance transition would greatly enhance NMR signals. In effect, as a consequence of electron–nuclear cross-relaxation, heating of electron spins produces a cooling of nuclear spins. That phenomenon became known as the Overhauser effect or, more generally, dynamic nuclear polarization. It is now widely used to enhance the sensitivity of NMR in many chemical and biological applications.

In 1957, almost simultaneously with the development of the theory of superconductivity by John Bardeen, Leon Cooper, and J. Robert Schrieffer, known as the BCS theory, Charlie and his student Charles Hebel measured the temperature dependence of the nuclear spin–lattice relaxation rate in aluminum above and below the 1.17 K superconducting transition temperature Tc. Their discovery of enhanced relaxation immediately below Tc, now known as the Hebel–Slichter peak, gave direct experimental support for the coherence factors that are unique to the BCS state’s pairing of electrons with opposite spins and momenta. The Hebel–Slichter data for spin–lattice relaxation in superconducting aluminum are arguably the most important single set of NMR data ever recorded.

Charlie and his students subsequently used NMR to probe electronic properties around magnetic impurities in metals, developed NMR methods to quantify slow atomic motions in solids, and used NMR to characterize charge density waves in transition-metal selenides. Beginning in the mid 1980s, Charlie and his group collaborated with John Sinfelt of Exxon Research on NMR studies of the structural and chemical properties of simple hydrocarbons on metal catalyst particles.

Following the discovery of high-Tc superconductors in 1986, Charlie returned to superconductivity research. In a series of papers between 1988 and 2012, he and his students and collaborators used NMR to elucidate important properties of spin susceptibilities, spin–spin couplings, and charge modulations in the normal and superconducting states of high-Tc cuprates. His group also provided some of the earliest evidence for unconventional pairing and magnetic structure in quasi-two-dimensional organic superconductors.

Charlie’s many honors include the 1969 Irving Langmuir Prize in Chemical Physics and the 1996 Oliver E. Buckley Condensed Matter Physics Prize, both from the American Physical Society, and the National Medal of Science in 2007. He was a member of President Lyndon B. Johnson’s Science Advisory Committee from 1965 to 1969, the National Science Board from 1975 to 1984, and the Harvard Corporation from 1970 to 1995.

Several generations of MR spectroscopists grew up on Charlie’s textbook Principles of Magnetic Resonance, which more than doubled in size from its initial publication in 1963 to its third edition in 1990. His deep understanding of physics, the breadth of his knowledge, and his outstanding mathematical abilities are evident in the classic book.

Charlie was a wonderful human being in every way, possessed of an unshakable optimism and generosity of spirit. To the end, he loved recounting stories about his supervisors John Van Vleck and Purcell, his undergraduate summers at Woods Hole, and his 63 graduate students and postdocs. He was always eager to engage students, younger colleagues, and casual acquaintances in discussions of topics both scientific and nonscientific. A favorite was the peculiar geometric properties of the martini glass, especially its third-power scaling of liquid volume with liquid height. He had a tradition of taking Polaroid photographs of visitors and posting them on the walls of his laboratory to teach his students that “science is done by real people.” Charlie will be deeply missed.