An international collaboration to advance condensed matter physics
(Top left to right): Jiaxin Zhang, Thibaut Divoux, Lucile Savary, Boris Shraiman, Ren-Bo Wang
(Bottom left to right): Antonin Roge, Peter Holdsworth, Leon Balents, Mark Bowick
Last year, KITP launched a new partnership with the CNRS, the French “National Science Research Center,” in the form of a new CNRS International Research Lab (IRL), called the French American Center for Theoretical Science (FACTS). It is based in Kohn Hall and entirely embedded in the scientific life of KITP.
The CNRS is the largest scientific institution in France and employs more than 25,000 researchers in all fields of science and humanities across the country. KITP is a familiar place to French physicists, with many coming every year to its programs for extended periods of time. Many of KITP’s faculty members have also had long-term collaborations with CNRS researchers, some who were postdoctoral researchers or graduate students at KITP or UCSB, in a wide variety of fields. These long-standing ties between French scientists and KITP and the commitment of scientists to work at Kohn Hall for at least six months—reflective of the institute’s mission since its inception to encourage collaboration through long stays—made the center’s location at KITP an obvious choice.
FACTS presently covers the fields of hard and soft/biological condensed matter theoretical physics. It is led by Lucile Savary, a CNRS researcher in hard condensed matter physics, and KITP Permanent Member Boris Shraiman. Additionally, the initiative can host up to three long-term senior members of the French scientific community who actively participate in KITP’s scientific programming and activities. At the time of writing, two scientists from Lyon, Thibaut Divoux and Peter Holdsworth, are at FACTS, as well as postdocs Ren-Bo Wang, Jiaxin Zhang and student Antonin Roge. Moreover, KITP Permanent Member Leon Balents and KITP Deputy Director Mark Bowick have also joined the center as local scientists. Applicants from France are selected once or twice per year by a scientific steering committee of scientists from MIT, Frankfurt University, the Collège de France, Flatiron Institute and the CEA (the French “Alternative Energy Commission”) who were selected for their expertise in the fields studied at FACTS.
Exciting new research is currently taking place at FACTS. Thibaut Divoux is working on rationalizing existing fractional rheological models by proposing a physical interpretation rooted in the study of superposition principles such as time-shear and time- aging in viscoelastic materials. This work helps establish a more physically grounded framework for interpreting the rheology of soft amorphous materials such as colloidal gels or soft glasses, and a student, Jacques Blin, will soon join him for a short visit.
Peter Holdsworth and Lucile Savary, together with visiting student Antonin Roge, are investigating new quantum states of magnets. With the growth of new “larger-spin” materials in experimental labs across the world, it is becoming crucial to develop theory to understand what new phases, qualitatively different from those already known, should appear in such materials.
Lucile Savary and her postdocs Jiaxin Zhang and Ren-Bo Wang are collaborating with KITP Permanent Member Leon Balents to try to better understand the role of quantum geometry in materials. The field of topology truly emerged in condensed matter in the last 3-4 decades, with many important workshops on this topic run at KITP. Only in the last few years have more subtle aspects of quantum geometry been discovered, in part via the recent breakthroughs in flat band materials growth. With this work, all members of FACTS continue pushing the boundaries of their fields.
FACTS Director and CNRS researcher Lucile Savary is originally from France but has spent a large fraction of her life in the United States on both the East and West Coasts and is very familiar with KITP and UCSB. She received her PhD from UCSB in 2014 and since then has spent several long-term visits at KITP for research programs, two of which she co-organized: Correlated Systems with Multicomponent Local Hilbert Spaces in 2020 and A New Spin on Quantum Magnets in 2023. From these visits and discussions during the weekly program barbecues at the Munger Physics Residence with other scientists, the idea of FACTS was born.
The administrative and funding structure for IRLs was already in place at CNRS, and the center’s leadership, along with KITP Director Lars Bildsten and UCSB Executive Vice Chancellor David Marshall, were very excited about the idea of this partnership between the two prestigious institutions. FACTS aims to strengthen ties in science between France and the US and international collaborations in general, while unifying less- studied aspects of condensed matter and biophysics fields.
by Lucile Savary
FACTS Director, CNRS Permanent Researcher