This award supports theoretical and computational research and education to study strongly correlated electron materials and to develop new theoretical and computational methods with an aim to develop a quantitative and microscopic theoretical framework to describe these materials. Strong correlations in solids drive a wealth of new and unusual physical properties, such as complex charge spin and orbital ordering, unconventional superconductivity, ultrafast nonlinear optical responses, large thermoelectric coefficients, huge volume collapses, and numerous metal-to-insulator transitions. The quantitative understanding of such properties and phenomena has proved to be a major challenge. The PI has been developing extensions of Dynamical Mean Field Theory. This approach reduces the complex many-body problem to a self-consistent finite cluster of sites embedded in a quantum medium. It provides a simpler picture of strongly correlated electron materials and allows computation of their physical properties in parameter regimes where standard theoretical methods fail to capture essential physics. The PI?s approach links low energy simplified pictures of the strong correlation phenomena to methods that model the microscopic complexity of real materials.
The PI will study complex strongly correlated materials of current experimental interest and of great fundamental importance. He will focus on many body problems and electronic structure problems posed by uranium- and cerium-based heavy Fermion systems, copper oxides and the recently discovered iron pnictide high temperature superconductors, as well as the physics of electron gases. This work will stimulate close interactions with experimentalists and material scientists.
The PI will continue to develop first-principles approaches for carrying out practical computation of the electronic structure of complex correlated materials as well as to develop techniques for solving the quantum many body problem in model Hamiltonians. He will carry out further developments of cluster dynamical mean field theory including methods for adding long wavelength fluctuations to the local physics and new slave particle methods to obtain analytic insights at low energies.
This award supports training post-doctoral associates, graduate and undergraduate students in advanced theoretical and computational condensed matter and materials physics. These individuals will develop broad skills to analyze and solve complex problems of import to our modern technological society.
NON-TECHNICAL SUMMARY This award supports theoretical and computational research and education to develop a quantitative and predictive theoretical framework for materials in which the interactions between electrons is very strong. Strong interactions lead to intriguing new states of electronic matter, new phenomena, and unusual materials properties. Example materials include high temperature superconductors which exhibit a cooperative electronic state which exhibits no resistance to the flow of electricity, and related compounds which have unusual electronic properties. Also included is a class of rare earth and actinide compounds which exhibit a variety of unusual superconducting, magnetic, and metallic states. Calculating the electronic properties of these materials is lies beyond the most powerful computers that exist today. The PI will pursue an approach that links simplified models that contain essential physics with the most powerful methods that can calculate electronic states for real materials in microscopic detail. His research further develops these methods and applies them to understand new experiments on these materials in a timely way.
This award supports training post-doctoral associates, graduate and undergraduate students in advanced theoretical and computational condensed matter and materials physics. These individuals will develop broad skills to analyze and solve complex problems of import to our modern technological society.
on NSF grant DMR- 090694. This project developed new theoretical concepts and computational techniques to model the properties of materials where the Coulomb interactions among the electrons plays a crucial role, and test the methods against experiments in key strongly correlated materials. We determined the evolution as a function of temperature of the f-and spd character of the carriers of electricity in heavy fermion materials. The theory was tested against the photoemission spectra of heavy fermion materials such CeCoIr5. We carried out the first theoretical study of a Ni analog of the coper oxide layers using spin density functional theory. We modeled the optical and thermoelectric properties of FeSi, using Dynamical Mean Field Theory, establishing the importance of the Hunds rule coupling to describe strongly correlated semiconductors. We discovered the important role of the Hunds rule coupling in controlling the physical properties of the iron pnictides high temperature superconductors and explored its implications for the neutron scattering and optical conductivity spectroscopies in FeBa2As2 and FeTe. We extended the study of correlated systems to a non equilibrium situation. We extended the Dynamical Mean Field Theory formalism (DMFT) to molecules coupled to a electrodes, with an eye towards applications in nano-electronics. By applying an electric field and inserting a coupling to a dissipative reservoir in the Hubbard model we carry out a detailed study of the steady state and found a quasi one dimensional electronic structure in large fields.
