# Leo Radzihovsky

Leo Radzihovsky is a Russian American condensed matter physicist and academic serving as a professor of Distinction in Physics at the University of Colorado Boulder.
Radzihovsky's theoretical research integrates classical and quantum aspects of condensed matter, revealing novel states of matter and phase transitions between them, driven by strong fluctuations and/or spatial heterogeneity. He has authored numerous journal articles in leading journals, delivered talks at conferences and workshops, and is the recipient of the LeRoy Apker Award, Jonsson Valedictorian Prize, NSF CAREER Award.
Radzihovsky is a Simons Foundation Investigator, a Fellow of the David and Lucile Packard Foundation, a Fellow of the American Physical Society, and an Alfred P. Sloan Research Fellow.

## Early life and education

Born in Saint Petersburg, Russia, Radzihovsky immigrated to the US in 1980. In 1988, he earned his B.S. and M.S. in physics with a minor in Electrical Engineering from Rensselaer Polytechnic Institute (RPI) and in summers worked as an intern at Monsanto as a chemical engineer and at AT&T Bell Labs at Holmdel NJ in 1988 where he researched picosecond pulse generation and compression in semiconductor lasers, and met his future wife, Lucy Pao, also a professor at CU Boulder in Electrical Engineering. After graduating from RPI, he received the 1989 LeRoy Apker National Award for best undergraduate physics research on electron transport in nondegenerate semiconductors. Having moved to Harvard to pursue his Ph.D. in physics, in 1989 he received an A.M. in Physics. In the summers of 1989 and 1990, he worked as a summer intern at the Hewlett-Packard Labs in Palo Alto, where he designed a femtosecond laser pulse autocorrelator and studied optical fiber nonlinear effects. He married Lucy in 1991, and continued living in Cambridge MA. He completed his Ph.D. at Harvard in 1993, supported by the Hertz Graduate Fellowship, and pursued a Postdoctoral Fellowship at the James Franck Institute at the University of Chicago.

## Career

Radzihovsky started his academic career as an assistant professor of physics at CU Boulder in 1995, was promoted to associate professor in 2001 and then to Professor in 2003, and was awarded a title of professor of distinction in 2023. He served as a visiting scholar at Harvard, Weizmann Institute of Science in Rehovot, Israel, and Miller Professor at the University of California, Berkeley, DITP Professor at Leiden University, and is a frequent visiting researcher at the Kavli Institute for Theoretical Physics in Santa Barbara.
At KITP he served as a member of the advisory board during 2013–2017, and its chair in 2015–2016. In 2000, he co-founded the Boulder School for Condensed Matter and Materials Physics, funded by the National Science Foundation, and has served as its director, annual organizer, and regular lecturer since then. Additionally, he has served as a Member at Large of the Executive Committee at APS from 2019 to 2022, and a member of the Oliver Buckley, Lars Onsager Prize (chair in 2009) and APS Fellow Committees. He has served as a member of the editorial board for the Annals of Physics (2001–2012) and on the board for the Annual Review of Condensed Matter Physics since 2015.

## Research

Integrating the classical and quantum aspects of condensed matter, Radzihovsky's theoretical research spans a broad range of phenomena of liquid crystals, pinned and driven elastic media, degenerate atomic gases, superconductors, magnetism, topological states of matter, and associated phase transitions. The unifying theme of these diverse phenomena is the strong role played by quantum and thermal fluctuations, and/or spatial heterogeneity.
Radzihovsky's theoretical research is focused on the interplay and synergy between classical "soft" and quantum "hard" condensed matter and macroscopic systems that consist of fluids and solids of strongly interacting constituents, be they electrons, atoms, molecules, or bacteria. He uses methods of many-body field theory and renormalization group to treat strong non-perturbative effects of fluctuations and nonlinearities that are at play in condensed matter systems. Many of such strongly fluctuating condensed matter systems form universal states that he dubbed critical matter.
In classic soft matter, Radzihovsky (with John Toner, Pierre Le Doussal, and David Nelson) has studied fluctuations, anisotropy, topological defects, and quenched disorder-driven phenomena in tensionless elastic membranes (realized by biological lipid bilayers, cytoskeletal networks, and single-atom thin graphene sheets). These include anomalous elasticity with universal negative Poisson ratio and length-scale dependent elastic moduli, wrinkling, buckling, glassiness, tubule ordering, and associated entropically driven phase transitions.
Radzihovsky (with John Toner, Leon Balents, and Cristina Marchetti) explored vortex glassy matter of type-II superconductors in magnetic field, charge density waves (CDW), Wigner and colloidal crystals pinned by a substrate and/or an ever-present random quenched disorder, and broadly researched non-equilibrium dynamics and phase transitions of such driven elastic media.
Radzihovsky (with John Toner) contributed to liquid crystal phases and their phase transitions. These include novel banana bent-core shaped mesogens (with Tom Lubensky), anti- and ferroelectric nematic and smectic phases, and spontaneously chiral and cholesteric liquid crystals (with Noel Clark). He also led studies of nematic and smectic liquid crystals confined inside random porous matrix of aerogel (with John Toner and Noel Clark) and, with his students, subjected to surface pinning by a heterogenous substrate (as in a laptop or iPhone display), and liquid crystalline elastomers and rubber.
In quantum hard matter, Radzihovsky's (with Victor Gurarie and Dan Sheehy) contributions included predictions about degenerate atomic gases (AMO systems) controlled by narrow Feshbach resonances, which he used to study BCS-BEC crossover in paired balanced fermionic superfluids. He showcased the latter to be a route to the long sought-after Fulde-Ferrel-Larkin-Ovchinikov (FFLO) "pair-density wave" state, at nonzero temperature predicted to be a charge-4e superconductor (with Ashvin Vishwanath), its exotic descendant states, and their quenched non-equilibrium dynamics and phase transitions. He further demonstrated finite-angular momentum Feshbach resonances as a mechanism toward a realization of topological paired superfluidity and concomitant Majorana vortex modes, of interest for topological quantum computing, as first proposed by Alexei Kitaev. Applying these Feshbach resonances to degenerate bosonic atom counterparts, he with his Ph.D. students predicted novel molecular and finite-momentum superfluid phases, with the former recently observed experimentally.
Radzihovsky (with Leon Balents) investigated transport and tunneling through quantum Hall (QH) bilayers, and (with Jason Alicea, Leon Balents, Matthew Fisher, and Arun Paramekanti) studied quantum "flocking" and non-equilibrium hydrodynamics in microwave-irradiated QH systems, (with Alan Dorsey) QH nematic in partially filled high Landau levels, and associated quantum phase transitions. He studied (with Sergey Syzranov and Victor Gurarie) disorder-driven quantum phase transitions in Dirac and Weyl semimetals.
Radzihovsky, with his students and postdoc Michael Pretko, pioneered the relation of gapless "fracton" states of matter as tensor-gauge theory duals of topological defects in quantum crystals, and their Higgs transitions as quantum melting into supersolid, smectic, and nematic states of matter.
Radzihovsky’s research has been supported by the National Science, Packard, Sloan, and most recently by the James Simons Foundation as the Simons Investigator.

## Awards and honors

* 1988 – LeRoy Apker Award, American Physical Society
* 1988 – Jonsson Valedictorian Prize, Rensselaer Polytechnic Institute
* 1996 – CAREER Award, National Science Foundation
* 1997 – Fellow, A. P. Sloan Foundation
* 1998 – Fellow, David and Lucile Packard Foundation
* 2003 – Fellow, American Physical Society
* 2014 – Simons Investigator in Physics, Simons Foundation
* 2023 – Professor of Distinction, University of Colorado

## Personal life

In 1995, Leo and his wife relocated to Boulder, CO, as faculty at the University of Colorado, where they have since resided while pursuing their respective research and teaching careers.

## Selected articles

* Le Doussal, P., & Radzihovsky, L. (1992). Self-consistent theory of polymerized membranes. Physical review letters, 69(8), 1209.
* Radzihovsky, L., & Toner, J. (1997). Nematic–to–Smectic-A Transition in Aerogel. Physical review letters, 79(21), 4214.
* Bellini, T., Radzihovsky, L., Toner, J., & Clark, N. A. (2001). Universality and scaling in the disordering of a smectic liquid crystal. Science, 294(5544), 1074-1079.
* Gurarie, V., Radzihovsky, L., & Andreev, A. V. (2005). Quantum phase transitions across a p-wave Feshbach resonance. Physical review letters, 94(23), 230403.
* Sheehy, D. E., & Radzihovsky, L. (2006). BEC-BCS crossover in “magnetized” Feshbach-resonantly paired superfluids. Physical review letters, 96(6), 060401.
* Gurarie, V., & Radzihovsky, L. (2007). Resonantly paired fermionic superfluids. Annals of Physics, 322(1), 2-119.
* Pretko, M., & Radzihovsky, L. (2018). Fracton-Elasticity Duality. Physical Review Letters. 120 (19): 195301.
* Agterberg, D. F., Davis, J. S., Edkins, S. D., Fradkin, E., Van Harlingen, D. J., Kivelson, S. A., ... Radzihovsky, L. & Wang, Y. (2020). The physics of pair-density waves: Cuprate superconductors and beyond. Annual Review of Condensed Matter Physics, 11, 231-270.