Nihat Berker
MEF University
“Ashkin-Teller Physics: Multicritical Phase Diagrams, Algebraic Order, Chaos, Tripling, and Spinodals, d=1 Finite-Temperature Ordering with Giant Reentrances from Renormalization Group”
Abstract
Recent renormalization-group calculations have hyperfolded interesting Ashkin-Teller model physics. Global phase diagrams with bicritical, tricritical, critical-end points, bounding first- and second-order phase transitions bounding different types of conventional and algebraic ordering have been calculated, including continuously variable XY degrees of freedom and 6-point interactions in triple-deck models. With quenched-random ferro and antiferromagnetic couplings, two distinct types of spin-glass chaos have been found. Spinodal and equilibrium phase diagrams have been calculated. With d=1 with long-range interactions, the hybrid Thouless point for the onset of finite-temperature phase transitions and an equivalent-neighbor regime before reaching equivalence has been found. In the spin-one version of the model, finite-temperature tricritical phase diagrams with giant reentrances have been found.
Nihat Berker is a Professor of Physics at MEF University (2026–) and also teaches at Istanbul Technical University. He served as Dean of the Faculty of Engineering and Natural Sciences at Kadir Has University (2017–2026), Rector of Sabancı University (2009–2016), and has been Professor Emeritus of Physics at the Massachusetts Institute of Technology since 2004. He has also served as Coordinator of the Council of Higher Education (YÖK) Program for Outstanding Students in Basic Sciences, Professor of Physics and Literature, and Dean of the Faculty of Science and Letters at Istanbul Technical University (2003–2004). He holds dual bachelor’s degrees in Physics and Chemistry from MIT, and earned his M.S. and Ph.D. in Physics from the University of Illinois at Urbana–Champaign. After postdoctoral research at Harvard University, he was on the faculty at MIT from 1979 to 1999, becoming a full professor from 1988 to 2004. He has also served as Head of the Physics Department and Dean at Istanbul Technical University, and as Professor at Koç University. His honors include the MIT Physics Department Buechner Teaching Award, the Alfred P. Sloan Fellowship, the TÜBİTAK Science Award, election as Fellow of the American Physical Society, the MIT School of Science Graduate Teaching Excellence Award, designation as a Distinguished Turkish Scientist by the Turkish Academy of Sciences, and the Humboldt Research Award—the first awarded to a scientist from Türkiye. He has been elected to the Turkish Academy of Sciences and Academia Europaea.
Date: 1 April 2026, Wednesday
Time: 15:30
Place: SA-240
All interested are cordially invited.