TITLE : Estimation of the screened Coulomb interaction and correlation enhanced electron-phonon coupling in FeSe/SrTiO3 at a magic angle using dynamical mean-field theory
ABSTRACT :
Accurate first-principles estimation of the screened Coulomb interaction (U) and electron-phonon coupling (EPC), which are both material- and method-dependent, is crucial for understanding correlated materials. The screening arises from physical processes not inherently captured by the many-body method, making the U method-dependent. In the case of the embedded dynamical mean-field theory (eDMFT), which employs quasi-localized atomic basis functions for the interaction part of the Hamiltonian and the full Kohn-Sham basis for the kinetic energy part, conventional screening estimation approaches are inadequate. In this work, we compute U using constrained eDMFT (cDMFT), which incorporates essential corrections that are often neglected in other methods, such as constrained-RPA or constrained-DFT methods. Notably, the dependence of U on material specifics is less pronounced in eDMFT compared to DFT+U, where fine-tuning is often required for high-throughput calculations. The cDMFT-derived U yields excellent agreement with photoemission experiments across a wide class of materials, ranging from 3d to 5d transition metal compounds, including correlated metals, Mott insulators, altermagnets, and unconventional superconductors. Using the estimated value of U from cDMFT, we developed a method to compute EPC in eDMFT. We performed first-principles eDMFT calculations to explain the superconductivity in the epitaxial growth of the single-layer FeX (X=S, Se, Te) on SrTiO3 (001) substrate, which facilitates the controlled distortion of the FeX4 tetrahedron. We demonstrate a unique superconducting dome where the superconducting gap peaks at a ‘magic’ angle of the FeX4 tetrahedron and the EPC for the A1g mode is maximized for the FeSe film. This finding reveals a significant role of electronic correlations in enhancing Cooper pairing in unconventional superconductors by strengthening the EPC.
ABOUT THE SPEAKER :
Dr. Antik Sihi completed his B.Sc (Honours) in Physics from Sripat Singh College, University of Kalyani in 2015. He carried out an Integrated Ph.D. (M.Sc + Ph.D.) in Physics at Indian Institute of Technology (IIT) Mandi and graduated in 2023. From January 2023 to February 2024, he pursued his first Postdoctoral research at School of Physics and Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) at Trinity College Dublin in Ireland under the supervision of Prof. Stefano Sanvito and Prof. Andrea Droghetti. Since March 2024, he is working as a Postdoctoral Research Associate at West Virginia University, USA in a joint project supervised by Prof. Subhasish Mandal (at West Virginia University) and Prof. Kristjan Haule (at Rutgers University) to develop a database for correlated materials using beyond-DFT methods, which is funded by U.S. National Science Foundation. His preliminary research interests are also focused on the development of various beyond-DFT electronic structure methods to understand the quantum many-body behaviors of magnetic and correlated materials as well as unconventional superconductors.
MEETING DETAILS :
Speaker: Dr. Antik Sihi, Postdoctoral Research Associate, Department of Physics and Astronomy, West Virginia University, USA
Venue: A4 conference room, South Campus, IIT Mandi
Date and Time: December 10 th, 2025, Wednesday| 4:00 pm (IST)