Robert H. Silsbee, a longtime professor of physics and an administrator at Cornell University, died quietly on 23 May 2019 in Ithaca, New York. Bob was born on 24 February 1929, in Washington, DC, the youngest son of Francis B. Silsbee, a distinguished physicist at the Bureau of Standards. Like his father and brother, Henry, Bob earned degrees in physics from Harvard. Bob completed his PhD in 1956 with thesis adviser Harvey Brooks. After a year at Oak Ridge, he joined Cornell in 1957, rising to professor in 1965.
Bob’s early research centered on electron spin resonance (ESR) and optical studies of defects in alkali halides, as typified by the F-center in KCl. His thesis at Harvard in 1956 was a study of the ESR of this defect: an electron trapped at an anion vacancy, typically produced by diffusing potassium metal into pure KCl. At Cornell, Bob discovered the zero-phonon line in the optical absorption of a related defect at low temperature, a strikingly sharp peak appearing at the long wavelength end of the broad spectrum, especially in KCl and LiF. This is a direct analog of the Mössbauer effect. The color-center work displayed rigorous theory along with down-to-earth experimental skill, good grounds for educating graduate students. Bob’s research greatly advanced understanding of the optical absorption and structure of defects in alkali halides.
In 1980 Bob conceived of a method for injecting and electronically detecting spins in metals. This idea came to fruition in his lab in 1985 and was the precursor to the field of “spintronics” and spin transistors. He also developed an early interest in the phenomenon of Coulomb blockade in tunneling, with his lab producing some of the first demonstrations in small metal particles embedded in aluminum oxide. This work later extended into tunneling studies of semiconductor quantum dots and of two-dimensional quantum Hall systems.
Bob gave his students challenging projects that often required creation of new apparatus and experimental methods. The spin-injection experiment required use of an ultrasensitive SQUID picovoltmeter. Bob emphasized creating new measurement electronics and other novel apparatus. Thesis research in his lab could involve a milling machine, an oxyacetylene torch, silver soldering, and gold plating, with results analyzed using a density-matrix calculation revealing spectral diffusion.
Bob was a master at seeing and describing—often in very simple pictures—concepts in physics, while also discovering nuances and subtlety. He had a strong passion for talking physics. There was always a scientific conversation going on, from the brown-bag lunch to the student seminar, and extending into his carpool to the South Hill of Ithaca with Cornell faculty colleagues Don Holcomb and Bob Cotts. Bob Silsbee enjoyed frequent and long one-on-one meetings with his students thinking about problem solving or coming up with new ideas. These meetings often contained extended periods of silence until the ultimate aha moment occurred. Bob had amazing patience and kindness in dealing with students and had an empathetic ear for their personal issues.
Bob had a life full of exploration. In 1975, during the Cultural Revolution, he went to China as part of a solid-state physics delegation of the National Academy of Sciences. He took several sabbaticals in Europe, one at Bell Labs, and a last one trekking with his wife, Ann Silsbee, in the mountains of Nepal. In summers in the 1980s, he frequently rode his bicycle between his home and campus and up and down a very big hill with a makeshift apparatus that strapped his Macintosh computer to his back. He loved to tinker, and this was clear to anyone who stepped into his office and noticed the Rube Goldberg mechanism that relied on the weight of a dry-cell battery to pull the office door shut. In the late 1990s, he and Jörg Dräger wrote computer simulations together with a book for students learning solid-state physics. Bob’s passion for doing and science never waned and, into retirement, he spent a substantial amount of time designing and creating exhibits for the Ithaca Sciencenter.
Bob had a love of music, and his publication list includes the essay “Musical Acoustics” in The New Harvard Dictionary of Music, published in 1986 by Harvard University Press. He shared this passion with Ann (who passed away in 2003), who was a pianist, composer, and poet, and he continued in his involvement in music in his later years as a member of a chorus.
