Department of Physics at the University of Illinois at Urbana-Champaign

Charles P. Slichter Research Achievements

Research Professor of Physics
and Center for Advanced Study Emeritus Professor of Physics and of Chemistry

With his students and post docs, Professor Slichter has employed nuclear magnetic resonance and electron spin resonance to study condensed matter physics, magnetic resonance, chemistry, and surface physics and chemistry. Some of the accomplishments are:

Condensed Matter Physics

• His measurements with Hebel of nuclear relaxation in superconductors gave the first proof of the correctness of the pairing concept of the Bardeen-Cooper-Schrieffer theory of superconductivity.
• With Schumacher, he measured for the first time the electron spin contribution to the magnetic susceptibility of metals, providing an important test of many body corrections to the Pauli theory.
• He was a pioneer in application of electron nuclear double resonance to the study of defects in insulating crystals.
• He was a pioneer in the discovery and use of satellite NMR of host atoms near magnetic atoms in dilute alloys to elucidate the Kondo effect.
• With Henry he developed the method of moments for the analysis of the effect of magnetic fields or applied stresses on the optical spectra of defects in crystals.
• He made the first measurements of the spin-flip scattering cross section of conduction electrons from atoms in metals.
• He pioneered study of charge density waves in solids, using NMR to confirm McMillan's concept of discommensurations and demonstrating the motion of charge density waves under the action of applied electric fields.
• With his students he has made extensive studies of cuprate high temperature superconductors, characterizing the electron state of the Cu, discovering the indirect coupling between Cu atoms and showing than it gave information about the real part of the electron spin susceptibility.
• With his students, he showed that in the cuprate superconducting state, the electrons form spin singlet pairs.
• With his students, he gave substantial early evidence from spin lattice and spin-spin relaxation times of Cu and O nuclei that the superconducting orbital pairing could not be s state and was probably d-state. This work was one of the first indications that the conventional BCS pairing did not hold for the cuprates.

Magnetic Resonance Methods

• A pioneer of double resonance, with Carver he performed the first electron-nuclear double resonance, and the first observation of dynamic polarization of nuclei, proving the correctness of Overhauser's theory.
• He developed the concept of the relaxation rate in the "rotating frame" T_1ρ, enabling him to extend by orders of magnitude the range of motion rates in solids measurable by NMR.
• He showed, using the concept of spin temperature, how to solve otherwise intractable problems such as calculation of spin-lattice relaxation in zero applied field, calculation of T_1ρ in the slow motion regime, and for analysis of nuclear-nuclear double-resonance.
• With Spokas, he introduced phase coherent NMR detection of pulsed NMR, making possible detection of NMR signals much weaker than noise. All modern NMR equipment employs phase coherent detection.

Chemistry

• With Gutowsky and McCall, he was co-discoverer of the indirect spin-spin (J)coupling in molecules a key tool for chemists determining structure of molecules. This discovery led to the RKKY theory of coupling in solids.
• His theory of chemical shifts of ¹⁹ F nuclei gave the first explanation of why atoms with p or d bonding electrons have such large chemical shifts.
• He gave the first detailed theory the effect of rate processes on NMR spectra, now widely used to study chemical rate processes in liquids.

Surface Physics and Chemistry

• With his students and in collaboration with Sinfelt, he discovered the NMR line of the surface layer of atoms in metals, using small clusters (20-40 Å site) of Pt supported on Al₂O₃ and SiO₂. He established the electronic characteristics of these materials, which are catalysts for many important chemical reactions.
• In collaboration with Sinfelt, he and his group made the first NMR determination of the structure of simple molecules (CO, C₂H₂, C₂H₄) adsorbed on these Pt surfaces, studying their bonding to the surfaces, their breakup under heating, measuring the existence of and diffusion rate of isolated C atoms in the surfaces. They also determined the rate of H and D exchange between adsorbed molecules and the surface as well as between the support and the surface.