Electronic Structure, Spectroscopy and Correlation Effects in Novel Materials

                                           Arun Bansil (Northeastern Univ.), PI; Robert S. Markiewicz (Northeastern Univ), Co-I

This program is targeted on electronic structure, spectroscopic studies, and correlation effects in a variety of novel materials of great  current interest. Spectroscopies resolved highly in momentum, energy and space are playing a key role in unraveling the nature of the ground state and excitation properties in wide classes of novel materials. The seminal insights thus obtained are of critical importance not only for answering some of the great fundamental questions facing condensed matter physics and materials science, but also for understanding and thus helping to design and develop new materials with desirable properties. However, spectroscopies do not provide a direct map of electronic states, but act as a very complex ‘filter’ or ‘mapping’ of the underlying spectrum. This connection between electronic states and measured spectra—called the ‘matrix element effect’—is in general an extremely complex function of the phase space of the experiment (e.g. energy/polarization of photons in photoemission), presenting both a challenge and an opportunity. So motivated, we are pursuing techniques for realistic treatment of electronic spectra of a wide variety of materials, which serve as a prelude to formulating and implementing methodologies for making direct connection with various spectroscopies such as ARPES, STS/STM, and inelastic light scattering. Specific systems are topological materials, including 2D films beyond graphene, novel superconductors, and nanocrystals, among others. Our goal is to exploit the strengths of various spectroscopies to piece together a complete picture of electronic states in systems of great current interest, enabling direct and sharpened confrontations with theoretical models, and also help advance the reach of various spectroscopies.

Within this overarching goal, the ongoing research involves the development and implementation of methodologies, enabling us to address new classes of problems and materials of intense current interest. We are exploring a new generation of first-principles, parameter-free, predictive modeling of the electronic, geometric and magnetic structures of cuprates and other complex materials, which have so far been considered to lie outside the scope of such treatment. In parallel, we are moving vigorously from DFT to ‘beyond DFT’ schemes, and to developing/implementing methodologies needed for unfolding the associated matrix element effects in ARPES, STM/STS, RIXS, and other spectroscopies, and innovative genomic approaches toward materials discovery. In this way, we will continue to predict interesting topological phases of 3D and 2D quantum matter, and address exciting questions on spin textures of Dirac cone states and their spectroscopic signatures, how spin-orbit coupling thin films behave under external electric and magnetic fields, and how the physics of self-energy and vertex corrections, superconducting orders, pseudogaps, impurities and nanoscale heterogeneities plays out with doping and temperature in correlated materials. Use-inspired components in our research involve modeling and advanced characterization of Li-battery materials using light scattering techniques, development of viable strategies for efficient, gate-controlled manipulation of spins, and modeling and interpretation of positron spectroscopies as unique probes of nanoparticle systems. We are also exploring the potential of high-resolution Compton scattering as a new spectroscopic window for probing topological materials, and of topological and non-topological states under high pressures.