Transport and Nonequilibrium Effects in Strongly Correlated Multilayer Nanostructure

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TECHNICAL SUMMARYThis award supports theoretical and computational research and educational activities related to the treatment of transport and nonlinear effects in multilayered devices composed of strongly correlated multilayers. New formalisms and computational algorithms will be developed and then applied to systems that are being investigated experimentally by leading experimental groups around the world.In particular, the work includes:(i) Development of a new method for numerical renormalization group calculations that removes the ad hoc broadening and is able to accurately treat both high and low energy scales, enabling calculation of dc transport in both insulators and Fermi liquids. (ii) Development of a Green's function based density functional theory approach for determining thermoelectric properties of multilayered systems. This technique will be used to formulate design rules for how to maintain (or increase) the Seebeck effect when thermoelectric materials are incorporated into multilayer structures designed to block phonon transport.(iii) Development of an exact non-equilibrium dynamical mean-field theory approach to determine the current-voltage characteristic of a multilayered device described by a current biased Falicov-Kimball model. A strong-coupling based approach for the non-equilibrium impurity problem (similar to a hybridization expansion for continuous time quantum Monte Carlo approaches) to treat Hubbard and periodic Anderson models at strong coupling and with large driving fields will also be examined.(iv) Investigation of strong correlation effects on the capacitance of a parallel plate capacitor in which the dielectric layers or the metallic plates are replaced by strongly correlated materials. This theoretical and computational work will be coordinated with experimental efforts, including those of Jochen Mannhart in Germany (capacitors), Yuji Matsuda in Japan (charge and heat transport in heavy fermion multilayers), and Doug Natelson at Rice University, US (switching effects in contacts and in the bulk of strongly correlated materials).This project supports the training of graduate students in computational physics, both in the academic research environment and through year-long research internships at the IBM Almaden Research Center. The project also provides research experiences for undergraduate students, who will learn about international collaboration in science through summer internships at the Institute for Physics in Zagreb, Croatia. By engaging in a summer project with Georgetown's Program on Science in the Public Interest, undergraduates will also have the opportunity to gain a deeper understanding of the role of science and scientists in society at large.NONTECHNICAL SUMMARYThis award supports theoretical and computational research and educational activities related to the treatment of charge and heat transport in devices composed of several layers in which electrons interact strongly with each other leading to highly correlated motion. These materials have a large sensitivity to their environment, which makes them suitable for use in so-called smart-material devices which can improve the way many different electronic devices work. New formalisms and computational algorithms will be developed and then applied to systems that are being investigated experimentally by leading experimental groups around the world. Some examples include (i) examining how capacitance (capacity to store charge) can be modified in these systems, (ii) examining heat-induced electrical current or electrical current-induced heat transport in such multi-layer systems of sizes some 100,000 times smaller than the human hair, and (iii) examining how Ohm's law (which states that the voltage drop across a resistor is linearly proportional to the current through it) is violated in these devices by studying the so-called non-linear effects, that could potentially lead to ultrafast electronic switches. This project supports the training of graduate students in computational physics, both in the academic research environment and through year-long research internships at the IBM Almaden Research Center. The project also provides research experiences for undergraduate students, who will learn about international collaboration in science through summer internships at the Institute for Physics in Zagreb, Croatia. By engaging in a summer project with Georgetown's Program on Science in the Public Interest, undergraduates will also have the opportunity to gain a deeper understanding of the role of science and scientists in society at large.