Huaiyu Wang

All Publications

• Decoding THz-Driven Dynamic Fingerprints of Ferroelectric Nanotwin Networks. Advanced materials (Deerfield Beach, Fla.) Li, X., Ross, A., Stoica, V. A., Das, S., Hazra, S., Wang, H. H., Padma, H., Hoffmann, M. C., Kramer, P., Song, S., Nelson, S., Sato, T., Zhu, D., Ramesh, R., Martin, L. W., Cao, Y., Freeland, J. W., Lindenberg, A. M., Wen, H., Chen, L. Q., Gopalan, V. 2026: e73118

  Abstract

  Ultrafast polarization dynamics in ferroelectrics are of considerable interest for high-speed tunable dielectrics and electro-optics. Extended domain wall networks formed in ferroelectric twin nanodomains can support collective dynamics in the terahertz regime but require techniques that track polarization and strain evolution driven by ultrafast stimulus. Here, we use multi-modal probing of THz-pulse-driven excitations in PbTiO3/SrTiO3 superlattices by combining X-ray free electron laser measurements that directly tracks lattice changes, with optical second harmonic generation that tracks the electronic potential coupled with the lattice potential. Dynamical phase-field modeling enables fingerprinting of these collective modes as superpositions of domain "breathing" through wall oscillations and polarization "rotations" with still walls. Ultrafast domain wall motion at 0.1-0.5 THz is observed at practical fields of 100 kV/cm with wall velocities of >4000 m/s, approaching typical speed of sound in PbTiO3. A unique "charging" mode is discovered that can electrically charge and discharge domain walls on ∼4 ps time scale thus dynamically tuning wall conductivity. Integrated experimental and theoretical fingerprinting of the dynamical landscape presented here enables ultrafast control of ferroics for high-speed microelectronics and optical applications.

  View details for DOI 10.1002/adma.73118

  View details for PubMedID 42068172

• Terahertz-field activation of polar skyrons. Nature communications Wang, H. H., Stoica, V. A., Dai, C., Paściak, M., Das, S., Yang, T., Gonçalves, M. A., Kulda, J., McCarter, M. R., Mangu, A., Cao, Y., Padma, H., Saha, U., Zhu, D., Sato, T., Song, S., Hoffmann, M. C., Kramer, P., Nelson, S., Sun, Y., Nguyen, Q., Zhang, Z., Ramesh, R., Martin, L. W., Lindenberg, A. M., Chen, L. Q., Freeland, J. W., Hlinka, J., Gopalan, V., Wen, H. 2025; 16 (1): 8994

  Abstract

  Unraveling collective modes arising from coupled degrees of freedom is crucial for understanding complex interactions in solids and developing new functionalities. Unique collective behaviors emerge when two degrees of freedom, ordered on distinct length scales, interact. Polar skyrmions, three-dimensional electric polarization textures in ferroelectric superlattices, disrupt the lattice continuity at the nanometer scale with nontrivial topology, leading to previously unexplored collective modes. Here, using terahertz-field excitation and femtosecond x-ray diffraction, we discover subterahertz collective modes, dubbed "skyrons", which appear as swirling patterns of atomic displacements functioning as atomic-scale gearsets. The key to activating skyrons is the use of the THz field that couples primarily to skyrmion domain walls. Momentum-resolved time-domain measurements of diffuse scattering reveal an avoided crossing in the dispersion relation of skyrons. Atomistic simulations and dynamical phase-field modeling provide microscopic insights into the three-dimensional crystallographic and polarization dynamics. The amplitude and dispersion of skyrons are demonstrated to be controlled by sample temperature and electric-field bias. The discovery of skyrons and their coupling with terahertz fields opens avenues for ultrafast control of topological polar structures.

  View details for DOI 10.1038/s41467-025-64033-6

  View details for PubMedID 41068083

  View details for PubMedCentralID 9228410

• Coupled order parameters and photoinduced domain walls in the charge density wave of (TaSe₄)₂I NPJ QUANTUM MATERIALS Duncan, R. A., Orenstein, G., Kim, S., Huang, Y., Wang, H., Teitelbaum, S. W., Stanton, J., Hurley, M., Miller, A., Leonard, N., Hanlon, D., Reis, D. A., Osaka, T., Kubota, Y., Togashi, T., Qu, K., Shoemaker, D. P., Sato, T., Trigo, M. 2025; 10 (1)

  View details for DOI 10.1038/s41535-025-00762-7

  View details for Web of Science ID 001479433100001

• Hidden domain boundary dynamics toward crystalline perfection. Proceedings of the National Academy of Sciences of the United States of America Mangu, A., Stoica, V. A., Zheng, H., Yang, T., Zhang, M., Wang, H. H., Zu, R., Nguyen, Q. L., Song, S., Das, S., Meisenheimer, P., Donoway, E., Chollet, M., Sun, Y., Turner, J. J., Freeland, J. W., Wen, H., Martin, L. W., Chen, L. Q., Gopalan, V., Zhu, D., Cao, Y., Lindenberg, A. M. 2025; 122 (2): e2407772122

  Abstract

  A central paradigm of nonequilibrium physics concerns the dynamics of heterogeneity and disorder, impacting processes ranging from the behavior of glasses to the emergent functionality of active matter. Understanding these complex mesoscopic systems requires probing the microscopic trajectories associated with irreversible processes, the role of fluctuations and entropy growth, and the timescales on which nonequilibrium responses are ultimately maintained. Approaches that illuminate these processes in model systems may enable a more general understanding of other heterogeneous nonequilibrium phenomena, and potentially define ultimate speed and energy cost limits for information processing technologies. Here, we apply ultrafast single-shot X-ray photon correlation spectroscopy to resolve the nonequilibrium, heterogeneous, and irreversible mesoscale dynamics during a light-induced phase transition in a (PbTiO3)16/(SrTiO3)16 superlattice. Such ferroelectric superlattice systems are a useful platform to study phase transitions and topological dynamics due to their high degree of tunability. This provides an approach for capturing the nucleation of the light-induced phase, the formation of transient mesoscale defects at the boundaries of the nuclei, and the eventual annihilation of these defects, even in systems with complex polarization topologies. We identify a nonequilibrium correlation response spanning >10 orders of magnitude in timescales, with multistep behavior similar to the plateaus observed in supercooled liquids and glasses. We further show how the observed time-dependent long-time correlations can be understood in terms of stochastic and non-Markovian dynamics of domain walls, encoded in waiting-time distributions with power-law tails. This work defines possibilities for probing the nonequilibrium and correlated dynamics of disordered and heterogeneous media.

  View details for DOI 10.1073/pnas.2407772122

  View details for PubMedID 39773030

• Non-equilibrium pathways to emergent polar supertextures. Nature materials Stoica, V. A., Yang, T., Das, S., Cao, Y., Wang, H. H., Kubota, Y., Dai, C., Padma, H., Sato, Y., Mangu, A., Nguyen, Q. L., Zhang, Z., Talreja, D., Zajac, M. E., Walko, D. A., DiChiara, A. D., Owada, S., Miyanishi, K., Tamasaku, K., Sato, T., Glownia, J. M., Esposito, V., Nelson, S., Hoffmann, M. C., Schaller, R. D., Lindenberg, A. M., Martin, L. W., Ramesh, R., Matsuda, I., Zhu, D., Chen, L. Q., Wen, H., Gopalan, V., Freeland, J. W. 2024

  Abstract

  Ultrafast stimuli can stabilize metastable states of matter inaccessible by equilibrium means. Establishing the spatiotemporal link between ultrafast excitation and metastability is crucial to understand these phenomena. Here we utilize single-shot optical pump-X-ray probe measurements to capture snapshots of the emergence of a persistent polar vortex supercrystal in a heterostructure that hosts a fine balance between built-in electrostatic and elastic frustrations by design. By perturbing this balance with photoinduced charges, an initially heterogeneous mixture of polar phase disorders within a few picoseconds, leading to a state composed of disordered ferroelectric and suppressed vortex orders. On the picosecond-nanosecond timescales, transient labyrinthine fluctuations develop, accompanied by the recovery of the vortex order. On longer timescales, these fluctuations are progressively quenched by dynamical strain modulations, which drive the collective emergence of a single vortex supercrystal phase. Our results, corroborated by dynamical phase-field modelling, reveal non-equilibrium pathways following the ultrafast excitation of designer systems to persistent metastability.

  View details for DOI 10.1038/s41563-024-01981-2

  View details for PubMedID 39317816

  View details for PubMedCentralID 8024274

• Strong electron-phonon coupling driven pseudogap modulation and density-wave fluctuations in a correlated polar metal. Nature communications Wang, H. H., Xiong, Y., Padma, H., Wang, Y., Wang, Z., Claes, R., Brunin, G., Min, L., Zu, R., Wetherington, M. T., Wang, Y., Mao, Z., Hautier, G., Chen, L., Dabo, I., Gopalan, V. 2023; 14 (1): 5769

  Abstract

  There is tremendous interest in employing collective excitations of thelattice, spin, charge, and orbitals to tune strongly correlated electronic phenomena. We report such an effect in a ruthenate, Ca3Ru2O7, where two phonons with strong electron-phonon coupling modulate the electronic pseudogap as well as mediate charge and spin density wave fluctuations. Combining temperature-dependent Raman spectroscopy with density functional theory reveals two phonons, B2P and B2M, that are strongly coupled to electrons and whose scattering intensities respectively dominate in the pseudogap versus the metallic phases. The B2P squeezes the octahedra along the out of plane c-axis, while the B2M elongates it, thus modulating the Ru 4d orbital splitting and the bandwidth of the in-plane electron hopping; Thus, B2P opens the pseudogap, while B2M closes it. Moreover, the B2 phonons mediate incoherent charge and spin density wave fluctuations, as evidenced by changes in the background electronic Raman scattering that exhibit unique symmetry signatures. The polar order breaks inversion symmetry, enabling infrared activity of these phonons, paving the way for coherent light-driven control of electronic transport.

  View details for DOI 10.1038/s41467-023-41460-x

  View details for PubMedID 37723139

• Bipolaronic Nature of the Pseudogap in Quasi-One-Dimensional (TaSe4)2I Revealed via Weak Photoexcitation. Nano letters Zhang, Y., Murthy, C., Kafle, T. R., You, W., Shi, X., Min, L., Wang, H. H., Li, N., Gopalan, V., Mao, Z., Rossnagel, K., Yang, L., Kapteyn, H., Nandkishore, R., Murnane, M. 2023

  Abstract

  The origin of the pseudogap in many strongly correlated materials has been a longstanding puzzle. Here, we present experimental evidence that many-body interactions among small Holstein polarons, i.e., the formation of bipolarons, are primarily responsible for the pseudogap in (TaSe4)2I. After weak photoexcitation of the material, we observe the appearance of both dispersive (single-particle bare band) and flat bands (single-polaron sub-bands) in the gap by using time- and angle-resolved photoemission spectroscopy. Based on Monte Carlo simulations of the Holstein model, we propose that the melting of pseudogap and emergence of new bands originate from a bipolaron to single-polaron crossover. We also observe dramatically different relaxation times for the excited in-gap states in (TaSe4)2I (∼600 fs) compared with another 1D material Rb0.3MoO3 (∼60 fs), which provides a new method for distinguishing between pseudogaps induced by polaronic or Luttinger-liquid many-body interactions.

  View details for DOI 10.1021/acs.nanolett.3c01078

  View details for PubMedID 37682637

• Large Exchange Coupling Between Localized Spins and Topological Bands in Magnetic Topological Insulator MnBi2 Te4. Advanced materials (Deerfield Beach, Fla.) Padmanabhan, H., Stoica, V. A., Kim, P. K., Poore, M., Yang, T., Shen, X., Reid, A. H., Lin, M., Park, S., Yang, J., Hugo Wang, H., Koocher, N. Z., Puggioni, D., Georgescu, A. B., Min, L., Lee, S. H., Mao, Z., Rondinelli, J. M., Lindenberg, A. M., Chen, L., Wang, X., Averitt, R. D., Freeland, J. W., Gopalan, V. 2022: e2202841

  Abstract

  Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi2 Te4 , an intrinsic antiferromagnetic topological insulator. To achieve this, a multimodal ultrafast approach is employed to interrogate optically induced nonequilibrium spin dynamics. Momentum-resolved ultrafast electron scattering and magneto-optic measurements show that Bi-Te p-like states comprising the bulk topological bands demagnetize via electron-phonon scattering at picosecond timescales. Localized Mn 3d spins, probed by ultrafast resonant X-ray scattering, are found to disorder concurrently with the p-like spins, despite being energetically decoupled from the optical excitation. These results, together with atomistic simulations, reveal that the exchange coupling between localized spins and the bulk topological bands is at least 100 times larger than the primary superexchange interaction, implying an optimal exchange gap of at least 25 meV in the topological surface states. By directly quantifying this exchange coupling, the study validates the materials-by-design strategy of utilizing localized magnetic order to create and manipulate magnetic topological phases, spanning static to ultrafast timescales. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202202841

  View details for PubMedID 36189841

• Computing diffraction patterns of microstructures from phase-field simulations ACTA MATERIALIA Yang, T., Dai, C., Stoica, V. A., Xue, F., Wang, H., Ji, Y., Gopalan, V., Chen, L. 2022; 239

  View details for DOI 10.1016/j.actamat.2022.118258

  View details for Web of Science ID 000862785400004

• Fe3-xInSnxO6 (x=0, 0.25, or 0.5): A Family of Corundum Derivatives with Sn-induced Polarization and Above Room Temperature Antiferromagnetic Ordering CHEMISTRY OF MATERIALS Frank, C. E., McCabe, E. E., Orlandi, F., Manuel, P., Tan, X., Deng, Z., Jin, C., Croft, M., Emge, T., Yu, S., Wang, H., Gopalan, V., Lapidus, S., Wu, M., Li, M., Gross, J., Burger, P., Mielewczyk-Gryn, A., Klimczuk, T., Xie, W., Walker, D., Greenblatt, M. 2022; 34 (11)

  View details for DOI 10.1021/acs.chemmater.2c00312

  View details for Web of Science ID 000811935700001

• SnP2S6: A Promising Infrared Nonlinear Optical Crystal with StrongNonresonant Second Harmonic Generation and Phase-Matchability ACS PHOTONICS He, J., Lee, S., Naccarato, F., Brunin, G., Zu, R., Wang, Y., Miao, L., Wang, H., Alem, N., Hautier, G., Rignanese, G., Mao, Z., Gopalan, V. 2022; 9 (5): 1724-1732

  View details for DOI 10.1021/acsphotonics.2c00131

  View details for Web of Science ID 000804570900030

• Interlayer magnetophononic coupling in MnBi2Te4. Nature communications Padmanabhan, H., Poore, M., Kim, P. K., Koocher, N. Z., Stoica, V. A., Puggioni, D., Hugo Wang, H., Shen, X., Reid, A. H., Gu, M., Wetherington, M., Lee, S. H., Schaller, R. D., Mao, Z., Lindenberg, A. M., Wang, X., Rondinelli, J. M., Averitt, R. D., Gopalan, V. 2022; 13 (1): 1929

  Abstract

  The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise 'forbidden' by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases.

  View details for DOI 10.1038/s41467-022-29545-5

  View details for PubMedID 35396393

• Low-temperature processed beta-phase In2Se3 ferroelectric semiconductor thin film transistors 2D MATERIALS Lee, S., Zhang, X., McKnight, T., Ramkorun, B., Wang, H., Gopalan, V., Redwing, J. M., Jackson, T. N. 2022; 9 (2)

  View details for DOI 10.1088/2053-1583/ac5b17

  View details for Web of Science ID 000772181700001

• Ultrasensitive electrode-free and co-catalyst-free detection of nanomoles per hour hydrogen evolution for the discovery of new photocatalysts REVIEW OF SCIENTIFIC INSTRUMENTS Wang, H., Katz, R., Fanghanel, J., Schaak, R. E., Gopalan, V. 2022; 93 (2): 025002

  Abstract

  High throughput theoretical methods are increasingly used to identify promising photocatalytic materials for hydrogen generation from water as a clean source of energy. While most promising water splitting candidates require co-catalyst loading and electrical biasing, computational costs to predict them a priori become large. It is, therefore, important to identify bare, bias-free semiconductor photocatalysts with small initial hydrogen production rates, often in the range of tens of nanomoles per hour, as these can become highly efficient with further co-catalyst loading and biasing. Here, we report a sensitive hydrogen detection system suitable for screening new photocatalysts. The hydrogen evolution rate of the prototypical rutile TiO2 loaded with 0.3 wt. % Pt is detected to be 78.0 ± 0.8 µmol/h/0.04 g, comparable with the rates reported in the literature. In contrast, sensitivity to an ultralow evolution rate of 11.4 ± 0.3 nmol/h/0.04 g is demonstrated for bare polycrystalline TiO2 without electrical bias. Two candidate photocatalysts, ZnFe2O4 (18.1 ± 0.2 nmol/h/0.04 g) and Ca2PbO4 (35.6 ± 0.5 nmol/h/0.04 g) without electrical bias or co-catalyst loading, are demonstrated to be potentially superior to bare TiO2. This work expands the techniques available for sensitive detection of photocatalytic processes toward much faster screening of new candidate photocatalytic materials in their bare state.

  View details for DOI 10.1063/5.0077650

  View details for Web of Science ID 000757593400005

  View details for PubMedID 35232165

• Optimizing accuracy and efficacy in data-driven materials discovery for the solar production of hydrogen ENERGY & ENVIRONMENTAL SCIENCE Xiong, Y., Campbell, Q. T., Fanghanel, J., Badding, C. K., Wang, H., Kirchner-Hall, N. E., Theibault, M. J., Timrov, I., Mondschein, J. S., Seth, K., Katz, R., Villarino, A., Pamuk, B., Penrod, M. E., Khan, M. M., Rivera, T., Smith, N. C., Quintana, X., Orbe, P., Fennie, C. J., Asem-Hiablie, S., Young, J. L., Deutsch, T. G., Cococcioni, M., Gopalan, V., Abruna, H. D., Schaak, R. E., Dabo, I. 2021; 14 (4): 2335-2348

  View details for DOI 10.1039/d0ee02984j

  View details for Web of Science ID 000639552100001

• Searching for New Ferroelectric Materials Using High-Throughput Databases: An Experimental Perspective on BiAlO₃ and BiInO₃ CHEMISTRY OF MATERIALS Acharya, M., Mack, S., Fernandez, A., Kim, J., Wang, H., Eriguchi, K., Meyers, D., Gopalan, V., Neaton, J., Martin, L. W. 2020; 32 (17): 7274-7283

  View details for DOI 10.1021/acs.chemmater.0c01770

  View details for Web of Science ID 000569075300017

• High-Pressure, High-Temperature Synthesis and Characterization of Polar and Magnetic LuCrWO₆ INORGANIC CHEMISTRY Kim, S., Tan, X., Frank, C. E., Deng, Z., Wang, H., Collins, L., Lapidus, S. H., Jin, C., Gopalan, V., Kalinin, S., Walker, D., Greenblatt, M. 2020; 59 (6): 3579-3584

  Abstract

  A new polar and magnetic oxide, LuCrWO6, was synthesized under high pressure (6 GPa) and high temperature (1673 K). LuCrWO6 is isostructural with the previously reported polar YCrWO6 (SG: Pna21, no. 33). The ordering of CrO6 and WO6 octahedra in the edge-shared dimers induce the polar structure. The effective size of rare earth, Ln cation does not seem to affect the symmetry of LnCrWO6. Second harmonic generation measurements of LuCrWO6 confirmed the noncentrosymmetric character and strong piezoelectric domains are observed from piezoresponse force microscopy at room temperature. LuCrWO6 exhibits antiferromagnetic behavior, TN, of ∼18 K with a Weiss temperature of -30.7 K.

  View details for DOI 10.1021/acs.inorgchem.9b02900

  View details for Web of Science ID 000526414000029

  View details for PubMedID 32100540

• Competing Polar and Antipolar Structures in the Ruddlesden-Popper Layered Perovskite Li2SrNb2O7. Chemistry of materials : a publication of the American Chemical Society Uppuluri, R., Akamatsu, H., Gupta, A. S., Wang, H., Brown, C. M., Lopez, K. E., Alem, N., Gopalan, V., Mallouk, T. E. 2019; 31 (12)

  Abstract

  Over the past few years, several studies have reported the existence of polar phases in n = 2 Ruddlesden-Popper layer perovskites by trilinear coupling of oxygen octahedral rotations (OOR) and polar distortions, a phenomenon termed as hybrid improper ferroelectricity. This phenomenon has opened an avenue to expand the available compositions of ferroelectric and piezoelectric layered oxides. In this study, we report a new polar n = 2 Ruddlesden-Popper layered niobate, Li2SrNb2O7, which undergoes a structural transformation to an antipolar phase when cooled to 90 K. This structural transition results from a change in the phase of rotation of the octahedral layers within the perovskite slabs across the interlayers. First-principles calculations predicted that the antipolar Pnam phase would compete with the polar A 2 1 a m phase and that both would be energetically lower than the previously assigned centrosymmetric Amam phase. This phase transition was experimentally observed by a combination of synchrotron X-ray diffraction, powder neutron diffraction, and electrical and nonlinear optical characterization techniques. The competition between symmetry breaking to yield polar layer perovskites and hybrid improper antiferroelectrics provides new insight into the rational design of antiferroelectric materials that can have applications as electrostatic capacitors for energy storage.

  View details for DOI 10.1021/acs.chemmater.9b00786

  View details for PubMedID 38915773

  View details for PubMedCentralID PMC11194745