Neil W. Ashcroft, the Horace White Professor of Physics Emeritus at Cornell University and a world-renowned theorist in Condensed Matter Physics, passed away at the age of 82 on March 15, 2021 in Ithaca, NY. He is survived by his wife of 60 years, Judith, and his sons Robert and Ian.

Ashcroft was born on November 27, 1938 in London. He received his Bachelor of Science in 1958 and his Master of Science in 1960, both from the University of New Zealand, and earned his Ph.D. from Cambridge University in 1964. After Research Associateships at the University of Chicago and Cornell University, he joined the faculty at Cornell University in 1966 where he remained throughout his career. Neil had a particular interest in matter under extreme conditions and was an inspiration to the new generation of scientists who shared his vision to shape the path for high-pressure research for many years to come.

Ashcroft’s most tangible legacy may have been his textbook Solid State Physics written in the late 1960s and first half of the 1970s in collaboration with David Mermin. Following its publication in 1976, the book enjoyed tremendous success and was immediately translated into Polish, Russian and Japanese, and later made its way into German, French and Portuguese, as well as physics classrooms all over the world. When Physics Today published an article in 2013 that both praised the book and questioned whether it should be updated to keep pace with scientific advances, Ashcroft wrote with characteristic elegance in response, “...laudatory comments about our book are generous in the extreme. David and I are both grateful, and together we hope that the aging process, of ourselves and of our textbook, will not unduly accelerate.”

David Mermin remarked “Neil Ashcroft was a colleague and close friend for over 50 years. The happiest years of my professional life were the six years Neil and I spent writing our book Solid State Physics. Neil had a wonderful sense of humor. The fun we were having permeates the book. It’s still thriving 45 years after it came out, still in its original edition. Unlike almost all technical books, I believe ours entertains the reader in much the same way that Neil and I entertained each other while writing it.”

Over the years Ashcroft’s research interests encompassed many areas, including: density functional theory, matter at extreme densities and in reduced dimensionality, strongly correlated many-particle systems, superlattice hetero-structures, metal-insulator transitions, metallic hydrogen and hydrogen-rich materials, high-temperature superconductivity, and the general theory of superconductivity.

Following his formal retirement in 2006, Ashcroft displayed an unexpected new burst of scientific activity. After a serendipitous meeting with Roald Hoffmann , the Frank H.T. Rhodes Professor in Humane Letters Emeritus (A&S) and 1981 Nobel Laureate in Chemistry, Ashcroft joined Hoffmann’s research group. Their interdisciplinary collaboration was so productive it amounted to a research renaissance for Ashcroft.

“In 47 joint scientific papers over 15 years and in countless group meetings, I and my coworkers learned from Neil Ashcroft. And so did the community – superconductivity in high hydrides, a field suggested by Neil, has just blossomed,” Hoffmann said. “Neil was wise and perceptive, fascinated by the border between Chemistry and Physics. Our collaborators and I valued his physical insight and remember his gentle wit. And miss him.”

Ashcroft not only helped shape the fundamentals of his field. He also had a knack for anticipating its future discoveries. For example, in 1968 he proposed that hydrogen - which is a gas at ambient conditions - could become metallic, and a high-temperature superconductor, at high pressures. And just in the past six years, Ashcroft’s suggestion, originally made two decades ago, that high-temperature superconductivity could also be found in hydrogen-rich materials at extreme pressure was realized when several research groups reported superconductivity at very high and even ambient temperatures.

Ashcroft served 1985-87 as Chair of the Division of Condensed Matter Physics, American Physical Society. He also played a vital role in launching the Cornell High Energy Synchrotron Source (CHESS), serving as its co-principal investigator and associate director from 1978 to 1989. He was also director of the Laboratory of Atomic and Solid State Physics from 1979 to 1984 and the Cornell Center for Materials Research from 1997 to 2000.

Among his many honors, Ashcroft was a member of the National Academy of Sciences, the American Association for the Advancement of Science, a fellow of the American Physical Society, an honorary fellow of the Royal Society of New Zealand, a foreign member of the Russian Academy of Sciences, a Guggenheim Memorial Fellow, and winner of the 2003 Bridgman Award in high pressure physics bestowed by the International Association for the Advancement of High Pressure Science and Technology (AIRAPT).

We will miss him greatly.

[This obituary has drawn heavily from an article by David Nutt in the March 23, 2021 issue of the Cornell Chronicle at Cornell University, Ithaca, NY, USA.]