Extra Seminar - Würzburg ToCoTronics Colloquium

Second-order electrical responses, such as the nonlinear Hall effect, constitute the go-to signature of inversion-symmetry breaking and are widely used in the characterization of complex materials. However, the measured transport signal is often contrained by symmetry and afflicted with a multitude of device-specific contributions, such that it can rarely be interpreted ipso facto.

This talk builds on recent experiments on KTaO3 interfaces which have shown second-harmonic resistivities with large, reproducible mesoscopic fluctuations that persist in macroscopically large devices and are ubiquitous across all studied surface orientations.

We propose a theory which explains these observations as robust, magnetic-field-driven interference patterns arising from local symmetry breaking, driven by incipient ferroelectric polarization which creates large Berry curvature dipole fluctuations.

By linking quantum geometry to thermodynamic lattice ordering, our findings suggest nonlinear conductance fluctuations as a powerful new characterization tool, capable of revealing local ordering in complex materials that remains fundamentally invisible to conventional probes.