Electron Energy Loss Spectroscopy of strongly correlated systems in infinite dimensions

We study the electron-energy loss spectra of strongly correlated electronic systems doped away from half-filling using dynamical mean-field theory ($d=\infty$). The formalism can be used to study the loss spectra in the optical (${\bf q=0}$) limit, where it is simply related to the optical response, and hence can be computed in an approximation-free way in $d=\infty$. We apply the general formalism to the one-band Hubbard model off $n=1$, with inclusion of site-diagonal randomness to simulate effects of doping. The interplay between the coherence induced plasmon feature and the incoherence-induced high energy continuum is explained in terms of the evolution in the local spectral density upon hole doping. Inclusion of static disorder is shown to result in qualitative changes in the low-energy features, in particular, to the overdamping of the plasmon feature, resulting in a completely incoherent response. The calculated EELS lineshapes are compared to experimentally observed EELS spectra for the normal state of the high-$T_{c}$ materials near optimal doping and good qualitative agreement is found.Comment: 5 pages, 3 figures, submitted to J. Phys. - Cond. Mat

Theory of Magnetic Fluctuations in Iron Pnictides

Magnetic fluctuations in an unconventional superconductor (U-SC) can distinguish between distinct proposals for the symmetry of the order parameter. Motivated thereby, we undertake a study magnetic fluctuations in Iron pnictides, tracking their evolution from the incoherent normal, pseudogapped metal, to the U-SC state. Within our proposal of extended-s-plus s_{xy} inplane gap with proximity-induced out-of-plane line nodes, (i) we describe the evolution of the spin-lattice relaxation rate, from a non-Korringa form in the normal state, to a power-law form in the U-SC in good agreement with experiment, and (ii) we predict a sharp resonance in the U-SC state along (\pi,\pi), but not along (\pi/2,0), along with modulated c-axis intensity in inelastic neutron scattering work as a specific and testable manifestation of our proposal.Comment: 4 pages, 3 figures - to be submitted to PR

Quantum Critical Phase and Lifshitz Transition in an Extended Periodic Anderson Model

We study the quantum phase transition in $f$-electron systems as a quantum Lifshitz transition driven by selective Mott localization in a realistic extended Anderson lattice model. Using DMFT, we find that a quantum critical {\it phase} with anomalous $\omega/T$ scaling separates a heavy Landau-Fermi liquid from ordered phase(s). Fermi surface reconstruction occurs via the interplay between, and penetration of the Green function zeros to the poles, leading to violation of Luttinger's theorem in the selective-Mott phase . We show how this naturally leads to scale-invariant responses in transport. Our work is represents a specific (DMFT) realization of the hidden-FL and FL$^{*}$ theories, and holds promise for study of "strange" metal phases in quantum matter.Comment: 8 pages,5 figure