# Berry-phase theory of polar discontinuities at oxide-oxide interfaces

## TL;DR

This paper develops a rigorous microscopic understanding of electric displacement fields at oxide interfaces, demonstrating the conservation of the longitudinal component and generalizing the locality principle in first-principles modeling.

## Contribution

It establishes a fundamental theory of polarization and electric displacement at oxide interfaces, extending the locality principle to charge-mismatched systems.

## Key findings

- Longitudinal D component is conserved at oxide interfaces.
- The theory applies to LAO/STO interfaces and superlattices.
- Generalizes the locality principle in first-principles calculations.

## Abstract

In the framework of the modern theory of polarization, we rigorously establish the microscopic nature of the electric displacement field D. In particular, we show that the longitudinal component of D is preserved at a coherent and insulating interface. To motivate and elucidate our derivation, we use the example of LAO/STO interfaces and superlattices, where the validity of the above conservation law is not immediately obvious. Our results generalize the "locality principle" of constrained-D density functional theory to the first-principles modeling of charge-mismatched systems.