Byeoksong Lee | Searcharxiv

arXiv2025

First-principles theory of ionic thermoelectricity

Symmetry plays a crucial role in shaping the theories of fundamental forces. For example, general covariance -- the equivalence of all possible coordinate systems of spacetime -- dictates the law of gravity. Here, we extend this concept to nonequilibrium thermodynamics by developing a theory of ionic thermoelectricity (thermoelectricity without electrons) in electronically gapped ionic conductors. Within the Green-Kubo formalism, we show that energy gauge invariance -- the equivalence of all possible ways of distributing energy among atoms -- primarily determines the expressions for ionic thermoelectric coefficients. This symmetry-dictated theory is generally applicable, regardless of specific ion transport mechanisms, and provides a rigorous conceptual and computational framework for describing ionic thermoelectricity from first principles.

cond-mat.mtrl-sci↗

arXiv2025

Theory of Slidetronics in Ferroelectric van der Waals Layers

Vertically stacked layers derived from non-ferroelectric monolayers offer a promising route to two-dimensional (2D) ferroelectrics, where polarization switching occurs via interlayer sliding at sub-unit cell scales. Here, we develop a theory of slidetronics based on the notion that sliding-induced switching $P \rightarrow P'$ can also be achieved by applying an appropriate point-group operator $G$ to the entire system, such that $P' = G P$. Interlayer sliding and the transformation induced by the generator $G$ are thus equivalent in describing the relationship between the initial and final layer configurations. From this symmetry principle, we deduce that slidetronics can be classified by generators $G$; the generator $G$ must act as a symmetry operator for the constituent layers, while it is not a symmetry operator for the stacked layers as a whole; for a given 2D material, $G$ determines the interlayer sliding required for polarization switching; and sliding-induced complete polarization inversion is impossible in bilayers but can be realized in multilayers (e.g., PdSe$_2$ trilayers). These findings provide a framework for designing 2D ferroelectrics with targeted polarization-switching properties, as demonstrated through case studies of real materials.

cond-mat.mtrl-sci↗