arXiv subjects

Mohit Tanwani

Publications and source records attributed to Mohit Tanwani.

3 recordsLinked to original sources

arXiv2026

Probing (sub)nanoscale ferrons in an electron microscope

Ferrons are collective excitations of polarization fluctuations that can enable terahertz communications and quantum transduction due to long propagation lengths. Although ferrons have been experimentally demonstrated in van der Waals ferroelectrics and relaxor ferroelectrics, there is no direct (sub)nanoscale experimental evidence of ferrons in three-dimensional ferroelectrics. Here, we detect two types of ferrons, Higgs and pseudo-Goldstone, at the (sub)nanoscale in lead titanate by measuring vibrational signals due to polarization fluctuations. By harnessing momentum transfer in electron energy loss spectroscopy (EELS), we directly distinguish between soft-phonons and ferrons. We observe that the Higgs mode originates from the soft optical phonon parallel to the polar axis, whereas the pseudo-Goldstone mode originates from the soft optical phonon perpendicular to the polarization axis. Together with Landau theory, Raman spectroscopy measurements, and EELS, we observe that Higgs group velocities, in the bulk limit, are eight times greater than those of out-of-plane soft phonons and the pseudo-Goldstone ferrons have group velocities six times greater than in-plane soft phonons due to long-range dipole interactions. We further show that the domain size confinement effects lead to doubling of the respective bulk ferron group velocities, reaching up to approximately 15 km per second (almost 15 times higher than the out-of-plane soft phonon modes). Overall, this study opens a pathway to the detection of ferrons in three-dimensional ferroelectrics with domain engineering as a promising avenue for terahertz communication and transduction.

cond-mat.mtrl-sci↗

arXiv2025

Harnessing the polar vortex motion in oxide heterostructures

Polar topology, an analogue of the magnetic topology, serves as a large playground for exotic physical phenomena with a wide range of multifunctional applications. Polar vortices and skyrmions are representative polar topologies that have been predicted to significantly enhance the functionality and information density of nanoelectronic devices due to their ultrasmall dimensions. Despite these advantages, the practical realization of polar topologies in devices is impeded by the intrinsic challenges associated with their controlled motion and manipulation. Therefore, harnessing vortex manipulation-such as motion, on demand creation, annihilation, and shape transformation-is essential for practical device integration. However, vortex motion is often challenged by intrinsic physical limitations in collective lattice distortions and strong pinning effects from the surrounding environment, which remains elusive. In this study, we present real time observation of vortex motion in PbTiO3/SrTiO3 heterostructures, achieved through the application of localized pulsed electric fields and trailing bias fields from a conductive tip. Notably, the vortices exhibit reversible motion in response to the field direction. Furthermore, by precisely manoeuvring the conductive Atomic-Force-Microscopy tip along specific trajectories, we achieved controlled vortex reshaping, with reconfigured vortices showing remarkable stability over extended periods. This underline physical mechanism is further pinpointed by phase-field simulations, which revealed that the motion of the vortex boundary is controlled through the switching of the zigzag patterns of the vortex core. This study highlights the feasibility of harnessing vortex dynamics through external stimuli, advancing the fundamental physical understanding and prospects for next-generation polar vortex-based nanoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2025

PTST: A polar topological structure toolkit and database

Ferroelectric oxide superlattices with complex topological structures such as vortices, skyrmions, and flux closure domains have garnered significant attention due to their fascinating properties and potential applications. However, progress in this field is often impeded by challenges such as limited data-sharing mechanisms, redundant data generation efforts, high barriers between simulations and experiments, and the underutilization of existing datasets. To address these challenges, we have created the Polar Topological Structure Toolbox and Database(PTST). This community driven repository compiles both standard datasets from high throughput phase field simulations and user submitted nonstandard datasets. The PTST utilizes a Global Local Transformer (GL Transformer) to classify polarization states by dividing each sample into spatial sub blocks and extracting hierarchical features, resulting in ten distinct topological categories. Through the PTST web interface, users can easily retrieve polarization data based on specific parameters or by matching experimental images. Additionally, a Binary Phase Diagram Generator allows users to create strain and electric field phase diagrams within seconds. By providing ready-to-use configurations and integrated machine-learning workflows, PTST significantly reduces computational load, streamlines reproducible research, and promotes deeper insights into ferroelectric topological transitions.

cond-mat.mtrl-sci↗