GERALD MAHAN

1937 - 2021

MAHAN--Gerald Dennis. November 24, 1937 -- November 21, 2021. Gerald D. Mahan, one of the most innovative and prolific theoretical physicists of his generation, passed away at home on November 21, 2021 in Acton, Massachusetts. He lost his battle with leukemia and died peacefully in his sleep with his three children visiting and wife at his side. Dr. Mahan was a condensed matter physicist who did pioneering science in transport and optical properties of materials and solid-state devices. He discovered and analyzed quantitatively entirely new and unexpected many-body effects in x-ray line shapes which have been experimentally verified and named after him. The x-ray edge theory, published in 1967, is his most famous paper. He published approximately 300 papers in refereed journals and has been cited over 30,000 times. His 10 most cited articles showed a range of interests and included Nanoscale Thermal Transport (2001), The Best Thermoelectric (1995), Excitations in Metals: Infinite Hole Mass (1967), Theory of Photoemission in Simple Metals (1970), Theory of Conduction in ZnO Varistors (1979), Good Thermoelectrics (1998), Minimum Thermal Conductivity of Superlattices (2000), Excitations in Degenerate Semiconductors (1967), Collective Vibrational Modes of Absorbed CO (1978) and Local Density Theory of Polarizability (1990). His first refereed paper was published in Physical Review Letters in 1963 and his last paper was published in 2020. He wrote six books explaining condensed matter theory and its associated mathematics, the most notable of which is Many Particle Physics. This book was updated several times and is considered a foundational explanation of many body theory and its mathematical underpinnings including Green's functions. Born in Portland, Oregon Dr. Mahan graduated valedictorian from Franklin High School. He studied physics at Harvard University and graduated magna cum laude in 1959. In 1964, under John Hopfield at the University of California, Berkeley he received his PhD in physics for explaining linear dispersion in excitations. Upon graduation he became a research scientist at General Electric's Corporate Research Laboratory. He worked full-time for General Electric until 1967 and then spent another 28 years working for them part-time (one of the longest part-time continuous relationships in GE research history). While at GE he pioneered the application of mathematical techniques developed by three Russians (Abrikosov, Gorkov and Dzyaloshinski) to adapt Green's functions to theoretical solid-state physics. The solutions using this method challenged the conventional wisdom. The x-ray edge theory was part of this work. The results produced using this method, while controversial at the time, were almost universally supported by later experimental results and eventually became accepted as fundamental mathematical techniques. In 1967, Dr. Mahan became a professor of physics at the University of Oregon. While at Oregon he continued his work on the x-ray edge and expanded it to include surface science and the microscopic theory of dielectrics. He was awarded a Research Fellowship from the Alfred Sloan Foundation and spent 1970 working at the Cavendish Laboratory of Cambridge University, England. Dr. Mahan became a professor at Indiana University in 1973. During his tenure at Indiana, he expanded his areas of work to include varistors, which he did in conjunction with colleagues from GE. He developed mathematical models that explained how varistors function (they are extremely non-linear devices) leading to substantial improvements in their effectiveness. He worked closely with Lloyd Chase and did the first Raman scattering of beta- aluminum which is used to make high-density solid-state batteries. He continued to expand his areas of interest and co-invented the time-dependent local density approximation (TDLDA) which built on Walter Kohn's work inventing local density approximation (LDA). He later wrote a book on the subject with Kumble Subbaswammy (a former PhD student) titled Local Density Theory of Polarizability. Dr. Subbaswammy is currently the Chancellor of the University of Massachusetts at Amherst. Dr. Mahan was committed to the development of scientific talent and had several post doctorate students while at Indiana. These included Steven Girvin, Wilfred Haensch, William Pardee, Ji-Wie Wu, Matts Jonsson and Petter Minnhagen. Steven Girvin, who, like Dr. Mahan, received his PhD under the guidance of John Hopfield, later won the Oliver E. Buckley Prize of the American Physical Society and is the Eugene Higgins Professor of Physics at Yale University. Wilfred Haensch did pioneering work with Dr. Mahan explaining the "current drag" problem in semi-conductors and separate work with Dr. Mahan using new analytical methods to explain the Quantum Bolzmann Equation (QBE) which describes the transport of electricity in heat and solids. During his tenure at Indiana, he was invited by Stig Lundqvist of Chalmers University and the Niels Bohr Institute to spend a sabbatical year working at Chalmers in Goteborg, Sweden. This fostered a long collaboration with Chalmers and Swedish physics. In 1984 the University of Tennessee and Oak Ridge National Laboratory created a joint Distinguished Scientist program to raise the quality and profile of science in Tennessee. Dr. Mahan was recruited as the first member of that program and moved to Tennessee. He continued his research but spent much of his time as a research manager. During Lamar Alexander's tenure as President of the University of Tennessee, he recruited Dr. Mahan to teach freshman physics, which he did for ten years. At that time, there were not many members of the National Academy of Science teaching freshman physics. In 2001, Dr. Mahan was recruited to join the faculty of Penn State University as a Distinguished Professor. He expanded his areas of expertise to include thermoelectrics and thermal transport systems in nanotubes. He worked with Peter Eklund on vibrational properties of carbon nanotubes and silicon nanowires. He retired from Penn State in 2016 and served as an adjunct professor at the Massachusetts Institute of Technology from 2016 until 2020. Dr. Mahan was recognized for his pioneering work. He was elected as a fellow of the American Physical Society (1974), member of the National Academy of Sciences (1995), American Academy of Arts and Sciences (2005), foreign member of the Royal Society of Arts and Sciences - Goteborg, Sweden (2008), and Erasmus Mundas Lecturer of the European Union (2011). He received an honorary doctorate from Chalmers University, Goteborg Sweden in 2016. Later in his career, Dr. Mahan served as a leader of scientific organizations both in the United States and globally. He served as a General Councillor (Board of Directors) of the American Physical Society. He served as Secretary (Head) of Section III of the National Academy of Science. Section III includes Applied Math, Computer Science, Engineering and Applied Physical Science. He also served as Secretary of Section 33 (Applied Physical Science). He served as the first Chairman of the International Center for Condensed Matter Physics (ICCMP) in Brazilia, Brazil. In his role as Chairman of ICCMP he traveled relentlessly to foster collaboration between South American and US and European physicists. In his personal time, Dr. Mahan was an active fly-fisherman, avid wood worker and hiker. He was an accomplished amateur soccer coach and was a youth coach for his son Roy and Todd Yeagley. Todd is the head coach of Indiana University's men's soccer team and the son of legendary soccer coach Jerry Yeagley. He claimed one of his greatest challenges was the responsibility of coaching Todd Yeagley. Dr, Mahan backpacked through much of Sierra Nevada, Pacific Northwest and Smokey mountains, built his own McKenzie river boat, ran many rivers in Alaska, furnished several houses with handcrafted furniture and attended an uncountable number of his children and grandchildren's sporting events. In his later years he and his wife explored the world, visiting all seven continents. He was a loving husband and father who was always available for a game of cards and ready with a joke. Dr. Mahan is survived by his wife of 56 years, Sally Ann Spaugh Mahan, his three children and six granddaughters. His children's family include his son Christopher, wife Merrill and daughters Emily, Caroline, Margaux and Piper; his daughter Susan, husband Steven Kirincich and daughters Sarah and Abigail; and son Roy and wife Kerrianne.