Mihir Date

Many-body correlations in van der Waals systems from interlayer interactions: In condensed matter physics, electron-electron and electron-phonon interactions are the cornerstone of strongly correlated phenomena. In a myriad of different emergent phases, these interactions manifest in physical systems in the form of Mott insulators and charge density waves (CDW), respectively. The fingerprints of these quantum phases are usually embedded in the electronic structure in the form of renormalized energy dispersions and spectral gaps at (and at times away from) the Fermi level. Experimentally, angle-resolved photoemission spectroscopy (ARPES) allows us to conveniently map the entire Fermi surface of the solid, offering direct access to the spectral function in the momentum and energy space. ARPES is a well-suited technique where creating a new surface is very convenient in ultrahigh vacuum conditions, such as in the case of layered or van der Waals (vdW) systems. In these systems, the electronic structure is usually dominated by the energy dispersion of electrons in each layer. Here, one can ask- can the in-plane electronic structure of candidate two-dimensional Mott insulators and charge density waves (CDW) be altered by interactions between adjacent van der Waals layers?
To answer this question, I use synchrotron ARPES at large scale facilities across Europe, where photon energy can be changed conveniently allowing us to probe the energy dispersion along the out-of-plane momentum direction. Alongside, I use first-principles based techniques such as density functional perturbation theory (DFPT) followed by diagrammatic approaches to treat electron-phonon interactions using the EPW code.