Aarushi Khandelwal

All Publications

• Strain-induced lead-free morphotropic phase boundary. Nature communications Ghanbari, R., Kp, H., Patel, K., Zhou, H., Zhou, T., Liu, R., Wu, L., Khandelwal, A., Crust, K. J., Hazra, S., Carroll, J., Meyers, C. J., Wang, J., Prosandeev, S., Qiao, H., Kim, Y. H., Nabei, Y., Chi, M., Sun, D., Balke, N., Holt, M., Gopalan, V., Spanier, J. E., Muller, D. A., Bellaiche, L., Hwang, H. Y., Xu, R. 2025; 16 (1): 7766

  Abstract

  Enhanced susceptibilities in ferroelectrics often arise near phase boundaries between competing ground states. While chemically-induced phase boundaries have enabled ultrahigh electrical and electromechanical responses in lead-based ferroelectrics, precise chemical tuning in lead-free alternatives, such as (K,Na)NbO3 thin films, remains challenging due to the high volatility of alkali metals. Here, we demonstrate strain-induced morphotropic phase boundary-like polymorphic nanodomain structures in chemically simple, lead-free, epitaxial NaNbO3 thin films. Combining ab initio simulations, thin-film epitaxy, scanning probe microscopy, synchrotron X-ray diffraction, and electron ptychography, we reveal a labyrinthine structure comprising coexisting monoclinic and bridging triclinic phases near a strain-induced phase boundary. The coexistence of energetically competing phases facilitates field-driven polarization rotation and phase transitions, giving rise to a multi-state polarization switching pathway and large enhancements in dielectric susceptibility and tunability across a broad frequency range. Our results open new possibilities for engineering lead-free thin films with enhanced functionalities for next-generation applications.

  View details for DOI 10.1038/s41467-025-63041-w

  View details for PubMedID 40835605

  View details for PubMedCentralID 8423788

• Electron ptychography reveals a ferroelectricity dominated by anion displacements. Nature materials Kp, H., Xu, R., Patel, K., Crust, K. J., Khandelwal, A., Zhang, C., Prosandeev, S., Zhou, H., Shao, Y. T., Bellaiche, L., Hwang, H. Y., Muller, D. A. 2025

  Abstract

  Sodium niobate, a lead-free ferroic material, hosts delicately balanced, competing order parameters, including ferroelectric states that can be stabilized by epitaxial strain. Here we show that the resulting macroscopic ferroelectricity exhibits an unconventional microscopic structure using multislice electron ptychography. This technique overcomes multiple scattering artefacts limiting conventional electron microscopy, enabling both lateral spatial resolution beyond the diffraction limit and recovery of three-dimensional structural information. These imaging capabilities allow us to separate the ferroelectric interior of the sample from the relaxed surface structure and identify the soft phonon mode and related structural distortions with picometre precision. Unlike conventional ferroelectric perovskites, we find that the polar distortion in this material involves minimal distortions of the cation sublattices and is instead dominated by anion displacements relative to the niobium sublattice. We establish limits on film thickness for interfacial octahedral rotation engineering and directly visualize a random octahedral rotation pattern, arising from the flat dispersion of the associated phonon mode.

  View details for DOI 10.1038/s41563-025-02205-x

  View details for PubMedID 40269146

  View details for PubMedCentralID 9834382

• Visualizing Polar Distortions and Interface Effects with Multislice Ptychography. Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada Harikrishnan, K. P., Li, Y. E., Crust, K. J., Khandelwal, A., Shao, Y. T., Chen, Z., Zhang, C., Guguschev, C., Xu, R., Hwang, H. Y., Schlom, D. G., Muller, D. A. 2023; 29 (Supplement_1): 1626-1627

  View details for DOI 10.1093/micmic/ozad067.835

  View details for PubMedID 37613802

• Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes. Advanced materials (Deerfield Beach, Fla.) Xu, R., Crust, K. J., Harbola, V., Arras, R., Patel, K. Y., Prosandeev, S., Cao, H., Shao, Y. T., Behera, P., Caretta, L., Kim, W. J., Khandelwal, A., Acharya, M., Wang, M. M., Liu, Y., Barnard, E. S., Raja, A., Martin, L. W., Gu, X. W., Zhou, H., Ramesh, R., Muller, D. A., Bellaiche, L., Hwang, H. Y. 2023: e2210562

  Abstract

  Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high energy-density storage applications, understanding their size effects would provide key information for optimizing device performances at small scales. Here, we investigate the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO3 membranes. Via a wide range of experimental and theoretical approaches, we probe an intriguing antiferroelectric-to-ferroelectric transition upon reducing membrane thickness. This size effect leads to a ferroelectric single-phase below 40 nm as well as a mixed-phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, we show that the antiferroelectric and ferroelectric orders are electrically switchable. First-principle calculations further reveal the observed transition is driven by the structural distortion arising from the membrane surface. Our work provides direct experimental evidence for intrinsic size-driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead-free oxides with the membrane platform. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202210562

  View details for PubMedID 36739113

• Coupled harmonic oscillator models for correlated plasmons in one-dimensional and quasi-one-dimensional systems. Journal of physics. Condensed matter : an Institute of Physics journal Khandelwal, A., Mohammad Tashrif, S., Rusydi, A. 2021

  Abstract

  A new phenomenon of correlated plasmons was first observed in the insulating phase of the Sr1-xNb1-yO3+ family [T. C. Asamara et al., Nat Commun 8, 15271 (2017)]. The correlated plasmons are tunable, have multiple plasmonic frequencies, and exhibit low loss - making them desirable in numerous plasmonic applications. However, their fundamental mechanism is yet to be explored. While conventional plasmons can be understood solely by considering long-range interactions, unconventional correlated plasmons arise in correlated electron systems and require consideration of the short-range interactions. Here, we report how the interplay of short-range and long-range interactions determines the correlated plasmon phenomena through a coupled harmonic oscillator model of both 1D and quasi-1D systems. In each system, the impact of various physical parameters like the number of oscillators, energy scale, free electron scattering parameter, quasi-particle concentration, charges, effective masses, and Coulomb interaction strengths are explored to gain an understanding of their impact on the complex dielectric function and loss function. We study both cases where the parameters are the same for all quasi-particles and where effective mass, Coulomb interaction strength, and charge are varied for individual quasi-particles. In an extended model of the quasi-1D system, we study both cases where the rung symmetry of all parameters is conserved and where it is broken. When rung symmetry is conserved, the overall trends in optical and plasmonic peaks are the same as the 1D model, though the peaks tend to shift to higher energies and amplitudes. When rung symmetry is broken, the quasi-1D behavior deviates significantly from the 1D model, including an increase in the maximum possible number of optical and plasmonic peaks. Overall, our results demonstrate the significance of the interplay of short-range and long-range interactions in determining the correlated plasmons and identifying how various parameters can be used to tune the resulting plasmons.

  View details for DOI 10.1088/1361-648X/ac19e4

  View details for PubMedID 34340220

• Correlated cation lattice symmetry and oxygen octahedral rotation in perovskite oxide heterostructures JOURNAL OF APPLIED PHYSICS Chen, P. F., Lan, D., Liu, C., Wu, X. H., Khandelwal, A., Li, M. S., Li, C. J., Yang, P., Yu, X. J., Chen, J. S., Pennycook, S. J., Ariando, A., Huang, Z., Chow, G. M. 2021; 129 (2)

  View details for DOI 10.1063/5.0035501

  View details for Web of Science ID 000608037900003

• A cost-effective quantum eraser demonstration Physics Education Khandelwal, A., Tan, J., Leong, T., Yang, Y., Venkatesan, T., Jani, H. 2021; 56 (3): 033007

  View details for DOI 10.1088/1361-6552/abea49

• Using demonstrations to explain abstract science concepts: Hands-on and online demonstration-based pedagogy for enhancing student engagement in physics. Jani, H., Khandelwal, A., Leong, T., Yang, Y., Venkatesan, T. National Institute of Education (Singapore). Singapore. 2020 ; Research Brief Series (2010-3093): 20-018