TITLE : Direct observation of the Lindhard continuum using Resonant Inelastic X-ray Scattering (RIXS)
ABSTRACT :
The most elementary low-energy excitations of a Fermi liquid are particle-hole excitations obtained by scattering a quasiparticle across the Fermi surface, which generally form a continuous, bounded region in energy and momentum space, known as the Lindhard continuum. Despite the ubiquitous nature of the continuum, direct spectroscopic signatures of the intraband excitations involved in it have remained elusive. In this talk, I will discuss our recent observation and analysis of a low-energy, linearly dispersing feature in the Resonant Inelastic X-ray Scattering (RIXS) spectrum of MgB2 and its connection to the continuum of particle-hole excitations in this material. Our detailed simulations of the experimental spectrum overlap significantly with the non-interacting Lindhard function, and the latter is found to be dominated by excitations of intra-band origin. Our analysis conclusively demonstrates that the low-energy feature observed in the RIXS spectrum of MgB2 directly maps out the Lindhard continuum in this material, constituting the first direct spectroscopic observation of the continuum. Further, our results establish RIXS as a powerful orbital-selective and momentum-sensitive probe of elementary charge dynamics, across families of weakly and strongly correlated materials.
ABOUT THE SPEAKER :
Dr. Sarbajaya Kundu completed her PhD from the Tata Institute of Fundamental Research (TIFR), Mumbai in September 2019, under the supervision of Prof. Vikram Tripathi, studying electronic interaction effects in strongly spin-orbit coupled systems. Following her PhD, she worked as an IQ Postdoctoral Fellow in the Department of Physics and Institut Quantique (IQ), Universite de Sherbrooke from October 2019 to July 2021, where her research was focused on electronic interaction effects and their interplay with electron-phonon coupling in Dirac and Weyl semimetals, as well as the development and benchmarking of a new computational method for strongly correlated electron systems. Next, she worked as a Dirac Postdoctoral Associate in the Department of Physics, University of Florida, from August 2021 to July 2024, where she examined the characteristic signatures of classical memory effects due to long-range disorder in the magnetoresistance of 3D conductors, using a modified semiclassical Boltzmann framework. From August 2024 to July 2026, she was a Postdoctoral Research Associate in the Department of Physics and Astronomy, University of Notre Dame, working on a broad range of problems in the area of Quantum Materials Theory. Her research interests include electronic correlations in topological matter, Kitaev materials, coupled Luttinger liquids, computational strong correlation physics, signatures of non-Markovian memory effects in transport and elementary excitations in quantum materials.
MEETING DETAILS :
Speaker: Dr. Sarbajaya Kundu, Postdoctoral Fellow, Department of Physics and Astronomy, University of Notre Dame, Indiana, USA
Venue: SC NKN South Campus, IIT Mandi
Date and Time: Oct 8, 2026, Thursday at 4:00 pm
