Shivaji Lal Sondhi, professor of physics, transfers to emeritus status after twenty-six years on the faculty of the Department of Physics. He retired as a Princeton faculty member on July 31, 2021, when he was appointed as Wykeham Professor in the Rudolf Peierls Centre for Theoretical Physics at the University of Oxford. 

Shivaji grew up in Delhi, India. After receiving his bachelor of science in physics from Hindu College, University of Delhi in 1984, he started his graduate study at the State University of New York at Stony Brook under the supervision of Steven Kivelson. He then moved with his advisor to the University of California-Los Angeles, where he received his Ph.D. in 1992. Shivaji spent three years as a postdoctoral researcher at the Institute for Condensed Matter Theory at the University of Illinois at Urbana-Champaign before joining the Princeton physics faculty as assistant professor in 1995. He was promoted to associate professor in 2001 and became professor of physics in 2006. 

Shivaji has worked across a wide range of topics in theoretical condensed matter physics, notably in the areas of topological phases of matter, strongly correlated electrons, and quantum magnetism. Over the past fifteen years, condensed matter research has gone through a golden period thanks to the discovery of many interesting new phases of matter, and of novel mathematical and physical ideas to study them based on topology, symmetry, and quantum entanglement. Shivaji and the condensed matter theory group at Princeton have been consistently at the forefront of these developments. More recently, his research activity has focused on the study of many-body quantum dynamics. 

Shivaji’s renowned discovery of new topologically stable configurations, called skyrmions, in the quantum Hall effect, done while he was still a graduate student, earned him the 1996 William L. McMillan Award from the University of Illinois “for outstanding contributions in Condensed Matter Physics.” He is also a recipient of an Alfred P. Sloan Fellowship, a David and Lucile Packard Fellowship, and a Humboldt Research Award from the Alexander von Humboldt Foundation. He was elected fellow of the American Physical Society in 2008. 

His seminal work in 2008 on magnetic monopoles in spin ice possibly made an even bigger splash. Magnetic monopoles are notably absent in conventional electro-magnetic systems, or rather, they cannot appear as individual charges but are always confined into dipole pairs. Shivaji and his collaborators showed that in the material known as spin ice, these magnetic dipoles can in fact be broken apart into freely moving magnetic charges. This surprising theoretical prediction created considerable excitement and was directly verified in experiments. The ingenious use of topology and symmetry in this work are characteristic of Shivaji’s brilliance and foreshadowed important new discoveries in condensed matter theory that would follow soon after. The discovery of monopoles in spin ice was recognized with the 2012 Condensed Matter Division Europhysics Prize awarded by the European Physical Society and was listed among the top ten breakthroughs in science in 2009 by Science magazine. Shivaji’s discovery was even mentioned in an episode of the popular sitcom “The Big Bang Theory.” 

The above works highlight only a small subset of Shivaji’s scholarly achievements and activities. Other influential works include his 2001 paper with Moessner on the identification of a resonating valence bond liquid phase in the triangular quantum dimer model and his work on the dynamics of systems that exhibit many-body localization. In 2016, while he was the Humboldt Professor at the Max Planck Institute in Germany, Shivaji provided the key theoretical insight that led to the creation of a new phase of matter called a “time crystal.” Time crystals feature atoms and molecules that, in addition to containing a pattern that repeats in space, contain a pattern that repeats over time. Their possible existence was first proposed by Nobel laureate Frank Wilczek in 2012, but initial proposals for realizing this physics in the laboratory were all shown to be inadequate. Shivaji and colleagues showed that a time crystal phase can in fact be realized in non-equilibrium many-body localized systems subject to a periodic drive. This insight soon led to the first creation and experimental verification of discrete time crystals. This work provided fundamental new lessons about the nature of matter, and the out-ofequilibrium setting has enabled the realization of exciting new phases of matter. The discovery of time crystal phase in driven systems was listed among the top ten breakthroughs in physics in 2017 by Physics World. 

Shivaji’s work is characterized by a high degree of originality, depth of insight, and versatility. He has command of all aspects of modern theoretical physics, including many-body theory, quantum field theory, quantum information theory, and computational complexity theory. In addition to 150 publications on condensed matter theory, his intellectual pursuits include scholarly and opinion articles on topics ranging from India’s nuclear bomb program to the challenges of higher education and the management of the COVID-19 pandemic in India. Given his exceptional range of interests, it is not coincidental that Shivaji was one of the founders of the Princeton Center for Theoretical Science and one of its inaugural faculty fellows from 2006 to 2008. 

Shivaji is also an exceptionally successful and inspiring mentor to his graduate students. The Ph.D. students he supervised over the past fifteen years, including Fiona Burnell, Chris Laumann, Siddharth Parameswaran, Anushya Chandran, and Vedika Khemani, have all launched successful faculty careers since and are making an impact on their own. Shivaji is an equally valuable resource to his postdoctoral mentees and his faculty colleagues. He cared deeply about the success and future direction of the department and stood out in faculty meetings by the clarity with which he could put other people’s research contributions in context and for rarely missing the chance to express his frank opinion with a sharp-witted sense of humor. 

In addition to his work on condensed matter theory, Shivaji is an active thinker about current issues and future directions of human society. From 2009 to 2021, he was director of the Center for International Security Studies program “India and the World,” which focuses attention on the rise of India and its implications for international security. As director, he organized an annual program on international relations and strategic affairs for a select group of Indian members of Parliament, who traveled to Princeton to interact with leading experts to discuss strategic issues involving India and the global community. Special events included a visit to campus in 2017 by Rahul Gandhi, during which he engaged with Shivaji in a discussion regarding India’s present and future. In total, forty-eight Indian members of Parliament have visited Princeton through the program, four of whom are now ministers in the Indian federal government. 

Shivaji was awarded a 2020 Leverhulme International Professorship that is held at the University of Oxford. 

Written by members of the Department of Physics faculty.