Physics Department -  Domain Walls by Design: From Ferroic Interfaces to Topological Quantum Matter

Abstract
Ordered materials often form domains corresponding to distinct configurations of an underlying order parameter. The interfaces between them can host atomic structures and electronic properties absent from either surrounding state. A central challenge is therefore to move beyond observing naturally yet randomly occurring domain walls, and to instead create, position and manipulate them deterministically, transforming emergent interfaces into programmable elements of quantum materials. In this seminar, I will illustrate this concept in two distinct material platforms. First, I will show how top-down ion implantation and bottom-up electrostatic nano-templating enable the deterministic creation and precise positioning of in-plane charged antiphase boundaries and chiral ferroelectric domain walls, respectively, revealed by correlated microscopy in BiFeO3 thin films, establishing routes towards controllable domain-wall nanoelectronics. I will then turn to the in-situ optical control of topological domain walls in twisted MoTe2 moiré superlattices. Zero-field switching of integer and fractional Chern ferromagnets, and spatially resolved manipulation of ferromagnetic domain walls are realized using circularly polarized light. These results pave the way to programmable Chern junctions. Together, by controlling the boundaries between ordered structural or quantum states, we can create functionalities that are absent from the homogeneous phases themselves. I will conclude by discussing how this strategy can be extended in future directions, including device-oriented cryogenic transmission electron microscopy, structure-guided discovery and control of emergent quantum matter.