Klaus W. Kehr, a theoretical condensed matter physicist with the Institute of Solid State Research at the Research Center Jülich in Germany, died 9 March 2000 in Cologne, Germany, after a battle with a short but malignant disease.
Klaus was born on 16 July 1934 in Nürnberg, Germany. He earned his diplom in physics in 1961 from the Technical University of Munich. He obtained his doctoral degree in physics from the same university in 1965. His doctoral work, performed under the supervision of Wilhelm Brenig, was on the theory of superfluid helium-2.
Klaus’s first research position was at the Max Planck Institute for Physics and Astronomy in Munich, where he conducted research in solid-state physics. He left that institute in 1969 for Cornell University, where he took a two-year position as research associate with the Laboratory of Atomic and Solid State Physics. On his return to Germany in 1971, he joined the newly founded department of solid-state physics at the Research Center Jülich as a scientific member. The intense interaction between experimentally and theoretically inclined researchers within this department initiated his lifelong interest in diffusion theory.
Klaus’s work was initially motivated by phenomenological considerations; he particularly attempted to understand neutron scattering results on hydrogen diffusion in metals. However, he very quickly put his models in a more general and mathematical framework, which made them applicable to a wide range of diffusion phenomena. He pursued and advanced the theory of diffusion processes throughout his scientific career. An outstanding example is his work on the dynamics of muon spin depolarization in the presence of disorder.
A successful researcher and gifted and dedicated academic teacher, Klaus obtained his lecturing qualification (habilitation) in 1975 from the University of Cologne. He was appointed as a professor of physics at Cologne in 1985. He also continued to work for the Research Center Jülich. The undergraduates whom he lectured at Cologne as well as the advanced students at the Research Center Jülich enjoyed and profited from his careful, pedagogic, and methodical approach, his obvious dedication to physics, and his subtle humor.
His insistence on clear presentation is evident in the more than 100 papers he wrote or cowrote. The review article “Diffusion in Regular and Disordered Lattices,” which he published together with Joseph Haus in Physics Reports in 1987, is an important reference work for condensed matter physicists.
Klaus had no ambition to become a powerful science administrator—he loved science and wanted to stay in it. But his sense of duty and responsibility toward the department of solid-state physics nevertheless led him to accept, on three occasions over the years, the position of acting director of the theory group of which he was a member; the various directors had left and could not be replaced quickly. Between 1976 and 1999, he guided the departmental staff with empathy, competence, and a penchant for perfection.
Visitors and students from abroad who initially were drawn to him because of his international reputation invariably left as friends and admirers because of his kindness and modesty combined with a sharp intellect, scientific prowess, and encyclopedic knowledge of his field. Communication with Klaus was easy because of his love for and versatility with foreign languages; for example, he could speak English, French, and Japanese.
When he retired on 31 July 1999, he was full of plans to continue scientific work at the institute and to spend more time with his family and on his passion for hiking and mountaineering. Sadly, he became ill and was unable to pursue those plans. His family and many friends worldwide will remember him as a warm-hearted man and an enthusiastic scientist.
