Shoucheng Zhang (1963–2018) Co-Discoverer of Topological Insulators

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COMMENT OBITUARY Shoucheng Zhang (1963–2018) Co-discoverer of topological insulators.

houcheng Zhang’s pioneering work we trust’, was characteristic of his thinking. helped to launch a new branch of It invested hundreds of millions of dollars physics devoted to a class of materials in more than 100 technology start-ups, Scalled topological insulators. Like all insu- including many working with blockchain lators, these materials do not conduct technology, artificial intelligence, big electricity in bulk, but do so at their sur- data and robotics. In recent years, he was faces — because of quantum-mechanical increasingly a public intellectual; many of phenomena best understood using tools his lectures can be viewed on YouTube. His from the mathematical field of topology. He numerous awards included a share of the was widely expected to share a Nobel Prize American Physical Society’s pre-eminent

in Physics for his role in the prediction and award for condensed-matter physics — the /GETTY POST THE WASHINGTON FOR NICK OTTO discovery of the first topological insulator, Oliver E. Buckley Prize — and the 2015 made of bilayers of the semiconductors Benjamin Franklin Medal in Physics. cadmium telluride and mercury telluride. Zhang met his wife, Barbara, in kindergar- He was 55 when he took his life on ten in Shanghai. She joined him at graduate 1 December 2018, following a period of school at Stony Brook (to study statistics, depression and insomnia. in her case), becoming a software engineer Zhang was born in Shanghai. His parents at IBM until her recent retirement. The were engineers. He largely skipped high warmth and hospitality of their household school, entering the physics programme at was legendary. Dinners were often shared Fudan University at the age of 15. Selected with many family members and myriad to finish his undergraduate study abroad, close friends from the many communities to he received his Diplom-Physiker from the which Shoucheng belonged. This personal Free University of Berlin. In 1983, aged 19, contact left an indelible impression, in par- he began a PhD on supergravity at the State ticular, on many of his students and postdocs. University of New York at Stony Brook, with called the quantum spin Hall effect. Always apparent was the love and mutual physicist Peter van Nieuwenhuizen. Late last year, he was exploring parti- pride between Shoucheng and his children, In Zhang’s final year, on the advice of cles called Majorana fermions, which were Brian (now doing a PhD in statistics at the his hero (and, later, friend) C. N. Yang, he mooted in 1937 as a (still unconfirmed) University of Oxford, UK) and Stephanie (a switched to condensed-matter physics theory of the neutrino. ‘Emergent Majorana master’s student in educational technology under my supervision. After a postdoc modes’ are predicted to occur at the edges of at Stanford). with J. Robert Schrieffer at the Institute topological superconductors — cousins of Enthusiastic and brilliantly creative, for Theoretical Physics at the University of topological insulators. Zhang proposed that Zhang had a deliberate style that combined California, Santa Barbara, he moved to the these exotic particles could be observed in a mathematical precision and elegance with a IBM Almaden Research Center in San Jose, device made of a conventional superconduc- close and direct connection to phenomena California, and then in 1993 to the physics tor on top of a film of yet another species of that were measurable experimentally. He department at Stanford University, where he topological insulator — one that exhibits the had an uncanny knack for spotting prom- remained until his death. ‘quantum anomalous Hall effect’. ising scientists, and was generous with his Zhang was a theoretician whose work Several of Zhang’s other works were also time and thought in mentoring them. He inspired many experiments. Conceptually, he foundational. I had the privilege to collabo- was a key catalyst of the mutually beneficial played a leading part in mapping a taxonomy rate with him on the theory of fractional relationship that has developed over the past of the various ‘species’ of topological insula- quantum Hall liquids (S. C. Zhang et al. Phys. two decades between the condensed-matter tor. He identified a key feature of electronic Rev. Lett. 62, 82–85; 1989). These are states physics communities in the United States structure — band inversion — that is central with a form of topological order that results and China. to transforming normal insulators into in a single electron breaking up into a set of Shoucheng was infectiously interested topological ones under certain conditions. emergent particles, each of which carries a in everything — from the philosophy of His studies also guided the discovery of fraction of the electron charge. The basic the Roman poet Lucretius to the seascape actual materials. In particular, in 2006 Zhang understanding of these states, for which our in Cabo San Lucas, Mexico. He is sorely and his co-authors predicted the existence Stanford colleague Bob Laughlin received missed. ■ of a topological insulator (B. A. Bernevig a Nobel Prize in Physics, ranks among the et al. Science 314, 1757–1761; 2006), which most important pillars of condensed-matter Steven Kivelson is professor of physics at led to an experimental study the follow- physics. I vividly recall the ‘aha’ moment Stanford University and a member of the ing year (on which he collaborated) that when Zhang, drawing on his background Stanford Institute of Theoretical Physics, achieved the first observation of such an in formal field theory, showed how the basic California, USA. He was Shoucheng Zhang’s insulator in nature (M. Koenig et al. Science physics of these states follows simply and adviser on condensed matter for the final 318, 766–770; 2007). The topological insu- intuitively from the resulting field equations. year of his PhD, and collaborated with him lator had near-perfect conduction at its In 2013, Zhang co-founded the venture- on many projects thereafter. surface edges thanks to a phenomenon capital firm DHVC, whose motto, ‘In math e-mail: [email protected]