Research Projects

Symmetry and its breaking are fundamental concepts that permeate the physical sciences. In condensed matter physics, ferroic orders are defined by the symmetry of their order parameters. The traditional ferroic orders: ferroelectricity and ferromagnetism break spatial inversion (SI) and broken time-reversal (TR) symmetries, respectively, enabling control via conjugate electric and magnetic fields and facilitating a wide range of technological applications. In contrast, ferroaxial (FA) order, one of the rarest and most recently discovered ferroic orders, arises from a toroidal arrangement (vortices) of electric dipoles and is defined by an axial vector order parameter. This order results from a rotational distortion that breaks mirror symmetry about a plane containing the rotation axis while preserving both SI and TR invariance. As a consequence, FA order is inaccessible to conventional field-based control, posing unique challenges for its study and manipulation. Remarkably, a structural ferroaxiality can couple to magnetic order, inducing ferroelectric (FE) order and mediate a multiferroic state. This provides a platform to explore the interplay between multiple order parameters and the potential to control FA order through FE tuning, thereby opening new avenues for advanced device functionalities. Nevertheless, the area of FA order and electric toroidal moments remain under-explored, and significant efforts are underway to harness their unique properties. Scientific rationale: Recent polarisation-sensitive optical spectroscopic studies like electric quadrupolar SHG and linear electrogyration have allowed its observation. To advance the field, several fundamental questions must now be addressed: Which structural dynamics modes (and their symmetries) drive ferroaxiality? Do FA soft phonon modes exist analogous to ferroelectric orders? How do FE domains evolve from FA domains in multiferroics, where both coexist and can they be controlled? The above-mentioned spectroscopic methods lack sensitivity to lattice dynamics and therefore inadequate for these purposes. Given that Raman scattering is inherently sensitive to lattice dynamics, we hypothesize that Circular Dichroic (CD) Raman microscopy, with its symmetry sensitivity and spatial mapping capabilities, will allow us to investigate FA order dynamics and its potential coupling to FE order. O1: Set up cryogenic and CD Raman microscopy and spatially resolve phonons within ferroaxial domains present in a pure ferroaxial phase. Novelty and impact: While ferroaxial phase transition have been confirmed, its underlying lattice dynamics has not been studied. The first objective of this work is to identify these dynamics. O2: Identify phonon modes and associated symmetries responsible for FA ordering and domains. Novelty and impact: Given the structural nature of FA order, it is indispensable to identify the phonons and their symmetries driving the transition. The novelty of this objective lies in the use of Raman scattering to detect and study the soft phonon modes across the FA phase transition. This would help in designing new FA materials where domain control via thermal cycling can be easily accessed. O3: Observe and/or control the FE domains within the FA domains, and study the phonon and magnon dynamics, especially near the onset of the multiferroic coupling. Novelty and impact: If a FA order is coupled to another ferroic order that has a conventional conjugate field it may be used to indirectly control the ferroaxial domains in the multiferroic state. This objective uniquely aims to investigate phonon dynamics within the coexisting FA and magnetic-FE domains and study their evolution through the formation of a multiferroic state. A high impact result of this study with potential application could be the FA domain control using conventional stimuli, despite the inherent SI and TR invariance of the FA order.