About

Venkatraman Gopalan is a Distinguished Professor of Materials Science and Engineering and of Physics at Penn State University, where he also serves as the Associate Head for Graduate Education and Chair of the Intercollege Graduate Degree Program in Materials Science and Engineering. He received his B.Tech. in Metallurgical Engineering from the Indian Institute of Technology, Chennai, in 1989, and his Ph.D. in Materials Science and Engineering from Cornell University in 1995. His postdoctoral work included research at Carnegie Mellon University and the Los Alamos National Laboratory, focusing on ferroelectrics and electro-optics. His research focuses on the science and technology of nonlinear optical materials, straddling the fields of materials science, physics, and optical engineering. Key areas include complex oxides exhibiting phenomena such as ferroelectricity, magnetism, and metal-insulator transitions, with investigations into emergent phenomena, metastable phases, and hidden phases using ultrafast light pulses and nanoscale scanning probe techniques. He also collaborates on the development of semiconductor fibers and metalattices, creating complex optical structures with applications in high-speed detection and mid-infrared imaging. Additionally, Gopalan's work involves the study of symmetry operations in materials, including the introduction of rotation reversal symmetry and distortion reversal symmetry, which have implications for understanding material phenomena involving magnetism and structural distortions. Throughout his career, Gopalan has been recognized with numerous awards, including the NSF CAREER award, the Robert R. Coble Award, and the Richard M. Fulrath award. He has published over 200 papers and contributed to five book chapters. He is a Fellow of the American Physical Society and has served on the editorial board of the Annual Reviews of Materials Research. His research aims to advance the understanding of complex materials and develop novel optical and electronic devices.

Research topics

• Materials science
• Chemistry
• Composite material
• Nanotechnology
• Optoelectronics
• Physics
• Condensed matter physics
• Optics
• Inorganic chemistry
• Engineering
• Mathematics
• Thermodynamics
• Quantum mechanics
• Chemical engineering
• Nuclear engineering

Selected publications

• Probing hidden symmetry via nonlinear transport in an altermagnet candidate Ca3Ru2O7

  Nature Communications · 2026-02-23 · 1 citations

  preprintOpen access

  X-ray and neutron diffraction are foundational tools for structure determination; however, their resolution limits can lead to misassignments in materials with subtle distortions. Here we demonstrate that nonlinear transport provides a powerful complementary approach to uncover hidden crystal symmetries, using Ca3Ru2O7 as a case study. Below the magnetic transition at TS = 48 K, our experiment reveals a previously overlooked lower-symmetry phase. This is evidenced by the emergence of longitudinal nonlinear resistance (NLR), indicating combined translational and time-reversal symmetry breaking, and thus rendering Ca3Ru2O7 an altermagnetic candidate in terms of symmetry classification. DFT calculation suggests that the lower-symmetry phase arises from an extremely subtle lattice distortion (~0.1 pm) below TS, below the detection limit of conventional diffraction. Moreover, NLR is accompanied by nonlinear Hall effect, both enhanced by the large quantum metric associated with Weyl chains. Our findings establish nonlinear transport as a sensitive probe of hidden symmetry breaking and highlight an alternative route to discovering altermagnetic states. Altermagnets are characterized by fully compensated magnetic moments yet break time-reversal symmetry, leading to symmetry-enforced momentum dependent spin splitting. While demonstrations of almagnetism have typically proceeded via spectroscopic probes like ARPES, here Mali, Zhao and coauthors show that nonlinear transport can serve as a sensitive probe to screen for altermagnetic candidates, using Ca3Ru2O7 as a case study.

  PublisherOA PDFDOI

• Probing hidden symmetry via nonlinear transport in an altermagnet candidate Ca3Ru2O7

  Nature Communications · 2026-02-23

  articleOpen access

  X-ray and neutron diffraction are foundational tools for structure determination; however, their resolution limits can lead to misassignments in materials with subtle distortions. Here we demonstrate that nonlinear transport provides a powerful complementary approach to uncover hidden crystal symmetries, using Ca₃Ru₂O₇ as a case study. Below the magnetic transition at T_S = 48 K, our experiment reveals a previously overlooked lower-symmetry phase. This is evidenced by the emergence of longitudinal nonlinear resistance (NLR), indicating combined translational and time-reversal symmetry breaking, and thus rendering Ca₃Ru₂O₇ an altermagnetic candidate in terms of symmetry classification. DFT calculation suggests that the lower-symmetry phase arises from an extremely subtle lattice distortion (~0.1 pm) below T_S, below the detection limit of conventional diffraction. Moreover, NLR is accompanied by nonlinear Hall effect, both enhanced by the large quantum metric associated with Weyl chains. Our findings establish nonlinear transport as a sensitive probe of hidden symmetry breaking and highlight an alternative route to discovering altermagnetic states.

  PublisherOA PDFDOI

• Decoding THz‐Driven Dynamic Fingerprints of Ferroelectric Nanotwin Networks

  Advanced Materials · 2026-05-02

  articleOpen accessSenior author

  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 PbTiO 3 /SrTiO 3 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 PbTiO 3 . 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.

  PublisherDOI

• Above Room Temperature Ferroelectricity in Epitaxially Strained KTaO3

  arXiv (Cornell University) · 2026-01-21

  preprintOpen access

  Epitaxial strain is a powerful means to engineer emergent phenomena in thin films and heterostructures. Here, we demonstrate that KTaO3, a cubic perovskite in bulk form, can be epitaxially strained into a highly tunable ferroelectric. KTaO3 films grown commensurate to SrTiO3 (001) substrates experience an in-plane strain of -2.1 % that transforms the cubic structure into a tetragonal polar phase with transition temperature of 475 K, consistent with our thermodynamic calculations. We show that the Curie temperature and the spontaneous electric polarization can be system- atically controlled with epitaxial strain. Scanning transmission electron microscopy reveals cooperative polar displacements of the potassium columns with respect to the neighboring tantalum columns at room temperature. Optical second-harmonic generation results are described by a tetragonal polar point group (4mm), indicating the emergence of a global polar ground state. We observe a ferroelectric hysteresis response, using metal-insulator-metal capacitor test structures. The results demon- strate a robust intrinsic ferroelectric state in epitaxially strained KTaO3 thin films.

  PublisherDOI

• Above Room Temperature Ferroelectricity in Epitaxially Strained KTaO3

  ArXiv.org · 2026-01-21

  articleOpen access

  Epitaxial strain is a powerful means to engineer emergent phenomena in thin films and heterostructures. Here, we demonstrate that KTaO3, a cubic perovskite in bulk form, can be epitaxially strained into a highly tunable ferroelectric. KTaO3 films grown commensurate to SrTiO3 (001) substrates experience an in-plane strain of -2.1 % that transforms the cubic structure into a tetragonal polar phase with transition temperature of 475 K, consistent with our thermodynamic calculations. We show that the Curie temperature and the spontaneous electric polarization can be system- atically controlled with epitaxial strain. Scanning transmission electron microscopy reveals cooperative polar displacements of the potassium columns with respect to the neighboring tantalum columns at room temperature. Optical second-harmonic generation results are described by a tetragonal polar point group (4mm), indicating the emergence of a global polar ground state. We observe a ferroelectric hysteresis response, using metal-insulator-metal capacitor test structures. The results demon- strate a robust intrinsic ferroelectric state in epitaxially strained KTaO3 thin films.

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• Phase Boundary Enabled High Dielectric Tunability in Ba ₁ ₋ _x Sr _x TiO ₃ Thin Films and their Integration on Silicon

  Advanced Materials · 2026-04-21

  article

  ABSTRACT Achieving ultra‐high dielectric tunability with robust temperature and frequency stability poses a key challenge for next‐generation microwave electronics and telecommunications devices. Likewise, the integration of such materials with silicon is critical for scalability, yet it remains a complex task. This work addresses these challenges by engineering high‐quality, lead‐free Ba 1‐ x Sr x TiO 3 (BST; x = 0.2–0.8) epitaxial thin films. Through systematic control of composition and epitaxial strain, we have experimentally revealed the coexistence of cubic, tetragonal, rhombohedral, and orthorhombic phases, forming a mixed‐phase state analogous to a morphotropic phase boundary (MPB). This phase coexistence results in exceptional dielectric properties, including ultra‐high tunability (∼91%) and a high breakdown electric field (∼800 kV/cm) at room temperature (10 kHz). The films exhibit good thermal (from 330 to 473 K) and frequency (10 kHz–1 MHz) stability. The robust dielectric tunability being associated with a diffuse‐phase transition at higher strontium concentrations, arising from dipole dispersion, leading to relaxor‐like behavior. Theoretical studies using effective‐Hamiltonian approaches confirm the emergence of the MPB‐like state and its role in enhanced dielectric permittivity and tunability. Finally, integration of these BST thin films onto silicon is demonstrated, highlighting the potential for scalability. These findings bridge the gap between material innovation and industrial implementation.

  PublisherDOI

• Proximity Ferroelectricity in Compositionally Graded Structures

  Advanced Electronic Materials · 2026-02-19

  articleOpen accessSenior author

  ABSTRACT Proximity ferroelectricity is a novel paradigm for inducing ferroelectricity in a non‐ferroelectric polar material, such as AlN or ZnO that are typically unswitchable with an external field below their dielectric breakdown field. When placed in direct contact with a thin switchable ferroelectric layer (such as Al 1‐x Sc x N or Zn 1‐x Mg x O), they become a practically switchable ferroelectric. Using the thermodynamic Landau‐Ginzburg‐Devonshire theory, in this work, we perform the finite element modeling of the polarization switching in the compositionally graded AlN‐Al 1‐x Sc x N, ZnO‐Zn 1‐x Mg x O, and MgO‐Zn 1‐x Mg x O structures sandwiched in both a parallel‐plate capacitor geometry as well as in a sharp probe‐planar electrode geometry. We reveal that the compositionally graded structure allows the simultaneous switching of spontaneous polarization in the whole system by a coercive field significantly lower than the electric breakdown field of unswitchable polar materials. The physical mechanism is the depolarization electric field determined by the gradient of chemical composition “x”. The field lowers the steepness of the switching barrier in the otherwise unswitchable parts of the compositionally graded AlN‐Al 1‐x Sc x N and ZnO‐Zn 1‐x Mg x O structures. In the MgO‐like regions of the compositionally graded MgO‐Zn 1‐x Mg x O structure, a shallow double‐well free energy potential emerges. Proximity ferroelectric switching of the compositionally graded structures placed in the probe‐electrode geometry occurs due to nanodomain formation under the tip. We predict that a gradient of chemical composition “x” significantly lowers effective coercive fields of the compositionally graded AlN‐Al 1‐x Sc x N and ZnO‐Zn 1‐x Mg x O structures compared to the coercive fields of the corresponding multilayers with a uniform chemical composition in each layer. A tip‐induced switching further lowers the coercive field, enabling control of ferroelectric domains in otherwise unswitchable compositionally graded structures, which can provide nanoscale domain control for memory, actuation, sensing, and optical applications.

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• High-entropy design of transition metal oxide semiconductors with ultra-low thermal conductivity

  Communications Materials · 2026-03-26

  articleOpen access

  Metal oxides are used in a broad array of technological applications. However, only a small subset of oxide materials are semiconducting, which limits the range of chemical compositions available for engineering. Here we demonstrate a strategy for driving insulating metal oxides into a semiconducting state with ultra-low thermal conductivity (less than 1 W/m/K) by introducing configurational entropy. This change in electronic character is facilitated by cation mixing in a high-entropy phase, which activates several microscopic mechanisms in electronic and vibrational subsystems that combine to dominate the observed electronic and thermal response of the material. The electronic mechanisms include increased crystal field splitting and electronegativity differences, the preservation of split-off states from parent phases, in-gap states induced by charge transfer between mixed cations, and orbital degeneracy lifting due to lattice distortion. The ultra-low thermal conductivity is attributed to a combination of phonon-defect and crystal momentum non-conserving three-phonon scattering events, both of which arise from chemical disorder. We establish and quantify these effects through co-validated experimental and theoretical analyses of the high-entropy wolframite oxide A6WO4 (A = Mn, Fe, Co, Ni, Cu, Zn). Our analyses suggest that the proposed mechanisms are readily generalizable to a range of functional materials, and could be especially valuable in designing thermoelectric materials, which require simultaneous engineering of semiconducting and thermal properties. Transition metal oxides are interesting for advancing technology as they can combine ease of synthesis, resilience to defects, and high environmental stability, yet few exhibit semiconducting properties, limiting their engineering potential. Here, the authors transform insulating oxides into semiconductors with ultra-low thermal conductivity by introducing configurational entropy, offering a generalizable approach to designing advanced thermoelectric materials with tailored electronic and thermal properties.

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• Switchable Polarization in an A-Site Deficient Perovskite through Vacancy and Cation Engineering

  Journal of the American Chemical Society · 2026-01-23

  article

  While defects are unavoidable in crystals and often detrimental to material performance, they can be a key ingredient for inducing functionalities when tailored. Here, we show that an A-site-deficient perovskite Y_1/3TaO₃ exhibits switching-like polarization response at room temperature in the <i>Pb</i>2₁<i>m</i> phase, enabled by ordered vacancies coupled with TaO₆ octahedral rotations. Defect-ordered perovskites are frequently trapped in centrosymmetric incommensurate states due to competing structural instabilities; we circumvent this by favoring rotational over off-centering instability through compositional selection. Unlike canonical improper ferroelectrics that are <i>ferrielectric</i>, the vanishing dipoles on vacancy layers in Y_1/3TaO₃ allow for a net ferroelectric alignment of local dipoles, resulting in enhanced polarization. Upon heating, Y_1/3TaO₃ transforms to a paraelectric incommensurate phase at ≃750 K, whose atomic arrangement mirrors the domain topology observed in hybrid improper ferroelectrics. Superspace analysis of the modulated phase reveals a route to improve room-temperature polarization, achieved through epitaxial strain, as confirmed by our lattice-dynamics calculations. This defect-ordering strategy should be generalizable to other improper ferroelectrics, including magnetoelectric multiferroics, providing a pathway to amplify otherwise limited macroscopic polarization.

  PublisherDOI

• Switchable Polarization in an A-Site Deficient Perovskite through Vacancy and Cation Engineering

  Journal of the American Chemical Society · 2026-01-23 · 1 citations

  articleOpen access

  While defects are unavoidable in crystals and often detrimental to material performance, they can be a key ingredient for inducing functionalities when tailored. Here, we show that an A-site-deficient perovskite Y1/3TaO3 exhibits switching-like polarization response at room temperature in the Pb21m phase, enabled by ordered vacancies coupled with TaO6 octahedral rotations. Defect-ordered perovskites are frequently trapped in centrosymmetric incommensurate states due to competing structural instabilities; we circumvent this by favoring rotational over off-centering instability through compositional selection. Unlike canonical improper ferroelectrics that are ferrielectric, the vanishing dipoles on vacancy layers in Y1/3TaO3 allow for a net ferroelectric alignment of local dipoles, resulting in enhanced polarization. Upon heating, Y1/3TaO3 transforms to a paraelectric incommensurate phase at ≃750 K, whose atomic arrangement mirrors the domain topology observed in hybrid improper ferroelectrics. Superspace analysis of the modulated phase reveals a route to improve room-temperature polarization, achieved through epitaxial strain, as confirmed by our lattice-dynamics calculations. This defect-ordering strategy should be generalizable to other improper ferroelectrics, including magnetoelectric multiferroics, providing a pathway to amplify otherwise limited macroscopic polarization.

  PublisherOA PDFDOI

Recent grants

• A Symmetry-Based Approach to Minimum Energy Pathways

  NSF · $420k · 2018–2023

• Superior Nonlinear Optical Single Crystals and An Open-Source Modeling Package for Classical and Quantum Light Generation

  NSF · $485k · 2022–2026

• Nonlinear Optical Probing of Ferroic and Multiferroic Domain Dynamics

  NSF · $235k · 2005–2009

• Materials World Network: New Insights into Ferroelectric Domain Walls: Extended Nanoscale Structure, Bloch-Like and Neel-Like Character, and Spatially Resolved Dynamics

  NSF · $584k · 2009–2013

• Materials World Network: Gradient-Enabled Ferroic Phenomena: Tunable Metastable States, Roto-Flexo, and Transport Properties

  NSF · $750k · 2012–2018

Frequent coauthors

• Darrell G. Schlom

  Leibniz Institute for Crystal Growth

  186 shared

• Long‐Qing Chen

  Pennsylvania State University

  113 shared

• Amit Kumar

  108 shared

• R. Ramesh

  99 shared

• Nikolas J. Podraza

  University of Toledo

  98 shared

• Lane W. Martin

  Lawrence Berkeley National Laboratory

  97 shared

• M. O. Ramı́rez

  96 shared

• J. L. Musfeldt

  University of Tennessee at Knoxville

  96 shared

Awards & honors

• NSF CAREER award (2000)
• Robert R. Coble Award from the American Ceramics Society (20…
• Corning Faculty Fellowship in Ceramic Sciences (2004)
• National Research Council Faculty Fellowship (2004)
• Wilson Award for Excellence in Research (2005)