Second harmonic generation on incommensurate structures: The case of multiferroic MnWO4

TL;DR

This paper investigates second harmonic generation in incommensurate multiferroic MnWO4, revealing two distinct contributions related to magnetic order and local symmetry, bridging nonlinear optics and incommensurate order in materials.

Contribution

It introduces a novel analysis distinguishing two SHG contributions in incommensurate magnetic structures, highlighting the breakdown of conventional symmetry analysis due to local environment effects.

Findings

Identification of two different SHG contributions in MnWO4

Demonstration of symmetry analysis limitations for local environments

Bridging nonlinear optics with incommensurate magnetic order

Abstract

A comprehensive analysis of optical second harmonic generation (SHG) on an incommensurate (IC) magnetically ordered state is presented using multiferroic MnWO4 as model compound. Two fundamentally different SHG contributions coupling to the primary IC magnetic order or to secondary commensurate projections of the IC state, respectively, are distinguished. Whereas the latter can be described within the formalism of the 122 commensurate magnetic point groups the former involves a breakdown of the conventional macroscopic symmetry analysis because of its sensitivity to the lower symmetry of the local environment in a crystal lattice. Our analysis thus foreshadows the fusion of the hitherto disjunct fields of nonlinear optics and IC order in condensed-matter systems.