Materials and Models for Coexisting Metallic Conductivity and Broken Inversion Symmetry

Hickox-Young, Daniel Timothy

doi:https://doi.org/10.21985/n2-r4wc-dw55

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Materials and Models for Coexisting Metallic Conductivity and Broken Inversion Symmetry

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Metallic conductivity and broken inversion symmetry were long thought to be contraindicated properties, under the assumption that long-range Coulombic interactions (screened by free charge carriers) were necessary for coordinated polar displacements. Within the past decade, the discovery of polar metals has prompted a rethinking of the relationship between metallicity and inversion-lifting distortions, spurring new research on diverse materials. Recent work has revealed that polar metals are capable of hosting a wide variety of rare and desirable properties, ranging from unconventional superconductivity to enhanced thermopower. Nonetheless, there remains ambiguity regarding the fundamental relationship between the distortion mechanism and the electronic structure, due in part to the many different approaches to uniting the two orders. Thus, despite a large number of so-called "ferroelectric," "ferroelectric-like," and "polar" metals, band metals that exhibit an inversion-breaking distortion are still rare. In this dissertation, I use first principles simulations to investigate the rich landscape of materials that combine long-range polar order with free charge carriers. The lack of clarity in this materials landscape limits our ability to maximize the potential technological impact of polar metals. Therefore, this work 1) classifies and categorizes the diverse methods of uniting broken inversion symmetry with metallic conductivity, 2) investigates the interplay between doped charge carriers and polar distortions, and 3) predicts a new class of polar metals. My efforts demonstrate that the fundamental relationship between conductivity and polar order depends on the materials class and distortion mechanism, and provides guidelines for the design of polar metals in new materials classes.

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