Can chirality in materials be a new order parameter?

Abstract

Chirality describes objects that cannot be superimposed onto their mirror image. It is a fundamental concept with implications in physics, chemistry, and biology. In crystalline solids, structural chirality can lead to a variety of interesting properties, including Natural Optical Activity (NOA). This thesis explores the possibility of treating chirality itself as a primary order parameter in displacive phase transitions (in analogy with polarization in ferroelectrics or magnetization in ferromagnets). Using tin(II) fluoride as a material of interest, it uses first-principles calculations based on Density Functional Theory and Density Functional Perturbation Theory to study a displacive transition. That transition follows a pathway from a hypothetical achiral parent phase to an experimentally observed chiral ground state. Along this pathway, the energy, the helicity (a quantification of chirality), and NOA are computed as functions of the distortion.