NSF/DMR-BSF: Quantum transport of charge and heat in correlated electron systems

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NONTECHNICAL SUMMARYThe National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US- and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on fundamental aspects of charge and heat transport in metallic systems. Measurements of electric currents that flow through a condensed matter system are often the tool of first resort for characterizing newly synthesized materials, or for gaininig deeper insights into the nature of interesting phases of matter. Often, measuring the flow of heat can provide valuable supplementary information, in particular in cases where quantum mechanical effects and interactions between the carriers are important. This is because heat currents can be driven even when electric charge carriers are immobile. While electric transport has been studied extensively in many systems, thermal or thermoelectric transport remains relatively poorly understood. To take full advantage of existing experimental techniques, it is therefore crucial to further improve our theoretical understanding of these transport processes. That is the main goal of this research project. In additional to its scientific merit, better knowledge of fundamental mechanisms of charge and heat transport, especially in semiconductors, holds promise for improving energy efficiency in electronic devices. Further impact of this activity will lie in training graduate students and postdoctoral fellows. Specifically, junior participants can greatly benefit from this international collaboration, which will allow them extended visits at a prestigious, non-US institute where they can be exposed to different ideas and approaches, and make connections that will help them in their future careers.TECHNICAL SUMMARYThe National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US- and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on thermal and thermoelectric transport in correlated electron systems. In correlated electron systems, thermal and thermoelectric transport coefficients offer complementary information as they probe different aspects of the electron dynamics. To take full advantage of these experimental techniques, it is crucial to further improve our theoretical understanding of transport processes involving both electric charge and heat. Theoretical understanding of transport in complex materials is often impeded by multiple factors including strong correlations, impurities, Fermi-surface geometry, and phonons. It is therefore important to study systems where only some of these complications occur and can be studied in isolation to gain insights that may then be applied to more complex systems. Following this strategy, the research will initially focus on the disordered electron liquid near the metal-insulator transition, and then branch out to include more exotic strongly correlated systems.The main goals of the research project are: (i) To study theoretically the temperature dependence of the thermopower on the metallic side of the metal-insulator transition in disordered electron liquids. In particular, we will explore possible violations of the Mott-relation and the role of particle-hole asymmetry. (ii) To explore the effects of strong interactions on electric and thermal transport. In two-dimensional electron liquids, we intend to explore electric transport at the crossover between the low-temperature regime dominated by impurity scattering and higher temperatures where electron-electron collisions prevail. For strongly correlated materials, the project will focus on the response to a nonuniform temperature, where similar mechanisms can be at work.Deepening our knowledge on fundamental mechanisms of thermoelectric and thermal transport, especially in semiconductors, may improve energy efficiency in electronic devices. In particular, thermoelectric coolers and generators could benefit from understanding how material properties like disorder, interactions or the distance from a critical point affect transport coefficients. Further impact of this activity will lie in training graduate students and postdoctoral fellows. Specifically, junior participants can greatly benefit from this international collaboration, which will allow them extended visits at a prestigious, non-US institute where they can be exposed to different ideas and approaches, and make connections that will help them in their future careers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.