Ramamoorthy Ramesh

Ramamoorthy Ramesh (born 1960) is an American materials scientist of Indian descent who has greatly advanced the synthesis, assembly and understanding of complex functional oxides, such as ferroelectric materials, laying the foundation for development and application of multiferroic materials. In particular, his work pioneered the development of ferroelectric perovskites, manganites with colossal magnetoresistance, and multiferroic oxides with great impact on the materials physics and with the potential for significant benefits for modern information technologies.

He is a Professor at the University of California Berkeley in the Departments of Materials Science and Engineering, and Physics. He also leads more than 500 scientists as the Associate Laboratory Director for Energy Technologies at the Lawrence Berkeley National Laboratory. He has published over 540 papers in internationally recognized journals which have been cited more than 54,000 times. He has been issued 27 patents, and his approach for fabricating ferroelectric materials for random access memory has been employed by the world’s largest memory manufacturers.

Training and Career

In 1980 Ramesh received his Bachelor in Science degree in Chemistry at Madras University in India. In 1983 he received his Bachelors degree in Metallurgy from the Indian Institute of Science in Bangalore. He received his Doctorate in Materials Science from the University of California, Berkeley in 1987. He then served as a Postdoctoral Associate at the National Center of Electron Microscopy in Lawrence Berkeley National Laboratory (LBNL). He went to Bell Communications Research (Bellcore) in 1989 and initiated research in several key electrical device technologies, including ferroelectric nonvolatile memories. Ramesh joined the University of Maryland in 1995 and was promoted to Professor in 1999 and Distinguished Professor in 2003. The following year he joined the University of California faculty in the Materials Science and Engineering and Physics departments, and now serves as Purnendu Chatterjee Chair in Energy Technologies.

He joined Lawrence Berkeley National Laboratory in 2004 as a Faculty Scientist and became Associate Laboratory Director (ALD) for Energy Technologies in 2014. In his capacity as ALD, he serves as a strategic leader for three Laboratory Divisions focused on Energy Technologies. The Energy Technologies Area conducts research for the U.S. Department of Energy other federal entities, as well as state governments, with a focus on California and the private sector.

Ramesh served under Energy Secretary Chu as the founding Director of the SunShot Initiative, which aimed to bring the cost of solar electricity down to grid parity by the end of the decade. One significant impact of his role as the director has been to strengthen the scientific foundations for solar energy research to elucidate the complex science underpinning this technology. Later he also served in a leadership position at Oak Ridge National Laboratory.

Ferroelectric Thin Film Nonvolatile Memory

Ramesh pioneered the development of thin film ferroelectric materials for random access memory (FRAMS), first at Bellcore’s Red Bank, New Jersey facility, and then at the University of Maryland. These efforts paved the way for a reliable, high-density memory technology. He was the first to demonstrate that conducting oxide electrodes eliminate the 30-year old problem of polarization fatigue, achieved through careful control of the physics of the electrode-ferroelectric interface (Appl. Phys. Lett., 1992; Appl. Phys. Lett., 1993). This was a critical step in the development of reliable FRAM devices and became used pervasively by many semiconductor companies such as Fujitsu, which has operated the world’s largest FRAM production line, as well as Texas Instruments and others, directly benefiting technology worldwide.

Ramesh’s subsequent work explored the fundamental limits of switching dynamics and demonstrated the fastest switching speed in ferroelectric thin films, another key element that enabled high speed, nonvolatile random access memories. His work has also demonstrated a novel approach to create high density ferroelectric capacitors directly on the structure of silicon complementary metal–oxide–semiconductor (Si-CMOS) through the introduction of novel conducting barrier layers (see “Ferroelectric capacitor heterostructure and method of making same,” U.S. 5479317 A, 1994). Ramesh holds over 20 patents in the field of ferroelectric thin films and devices.

Colossal Magnetoresistance

Beginning in 1993, Ramesh collaborated with SungHo Jin (Bell Labs) to initiate joint research into manganite thin films. They epitaxially grew lanthanum calcium manganite films, with detailed measurements of resistivity responses to magnetic fields, observing huge changes in resistance (Science, 1994). They coined the term Colossal Magnetoresistance (Science 1994) and this seminal paper has been cited more than 4,000 times, launching an international research effort on these CMR materials.

Ramesh and his collaborators also demonstrated several new device concepts, including a markedly improved, nonvolatile ferroelectric field effect device constructed of perovskite heterostructures with a highly magnetoresistive manganite as the channel semiconductor. In this case, he used lanthanum calcium manganite as the semiconductor and lead zirconate titanate as the ferroelectric gate (Science 1997). The carrier concentration of the semiconductor channel can be “tuned” by varying the manganite stochiometry. The enhanced interface characteristics enabled the fabrication of novel field effect devices.

Multiferroic Materials

In 2000, Ramesh began new explorations of coupled phenomena in complex oxides to develop the possibility of controlling ferromagnetism with an electric field. He was the first to discover large ferroelectric polarization in epitaxially grown thin films of bismuth ferrite (Science, 2003). He grew phase-pure BFO films in the thickness tens of nanometers by pulsed laser deposition. This work has stimulated a global research effort and has been cited more than 3,800 times, providing direct evidence of a very large spontaneous polarization in this ferroelectromagnet system, ideal for the development of sensors and actuators as well as electric field controlled magnetism.

Subsequently Ramesh and his colleagues prepared three-dimensional epitaxial nanocomposite of cobalt ferrite/barium titanate (Science, 2004). The self-assembled arrays of Cobalt ferrite nanopillars were embedded in the Barium titanate matrix. This approach to nanocomposite structures became quite generalized, with many others creating similar structures. This class of material facilitates the inter-conversion of energies stored in electric and magnetic fields and can play an important role in many devices.

His group also discovered a completely unexplored aspect of these materials, namely that ferroelectric domain walls in such multiferroics are electrically conducting [Nature Materials 8,(2009); Nature Materials 12, (2012); Reviews of Modern Physics, 84(2012)]. This discovery once again opened up a new avenue for worldwide research activity; many groups around the world are now actively engaged in exploring the intricacies and potential technological impact of such exotic phenomena. Following up on this work, his group demonstrated that such domain walls also exhibit anomalously large photovoltages [Nature Nanotechnology 5 (2010)] as well as the discovery of a new “super-tetragonal” phase of BiFeO3 [Science 326(2009)]. His research is now focused on exploring magnetotransport phenomena at such domain walls; for example, his group has shown that certain types of domain walls can be magnetic and thus also exhibit large magnetoresistance phenomena.

He is also focused on making Multiferroics and Magnetoelectrics a technological reality. In a development that holds promise for future magnetic memory and logic devices, Ramesh and his colleagues used an electric field to reverse the magnetization direction in a multiferroic material, pointing to a avenue towards spintronics and smaller, faster and cheaper ways of storing and processing data. They used heterostructures of bismuth ferrite and cobalt iron to fabricate a spin-valve this new spin valve (Nature, 2014). Ramesh’s research is now focused on exploring magnetotransport phenomena in multiferroic domain walls. For example, his group has shown that certain types of domain walls can be magnetic, and thus also exhibit large magnetoresistance phenomena. His most recent work (Nature, 2016) demonstrated the existence of polar vortices in ferroic superlattices, which could find potential applications for ultracompact data storage and processing.

New Photovoltaic Materials

Ramesh also developed bismuth ferrite materials as a type of photovoltaic material that produces voltages significantly higher than a typical semiconductor. He and his colleagues discovered a fundamentally new mechanism for photovoltaic charge separation, which operates over a distance of one to two nanometers and produces voltages that are significantly higher than conventional devices (Nat. Nanotechnology, 2010). This new degree of control, and the high voltages produced, may find application in photovoltaic cells and other optoelectronic devices.

U.S. Patents

Ramesh holds 27 patents, primarily in the field of ferroelectric thin films and devices. Examples include:

· “Growth of a,b-axis oriented perovskite thin films,” U.S. Patent No. 5358927, Issued 25 October 1994, A.Inam, R.Ramesh and C.T.Rogers

· “Epitaxial Ferromagnetic Manganese Aluminum Magnetic memory element and method for the preparation thereof,” U.S.Patent No.5169485, Dec. 8, 1992, S.J.Allen, J.Harbison, M.Leadbeater, R.Ramesh and T.D.Sands

· “Crystalline ferroelectrics grown on silicon dioxide,” U.S.Patent No. 5248564, 28 September 1993, R.Ramesh

· “Barrier layer for ferroelectric capacitor integrated on silicon,” R. Ramesh, patent No. 5838035, 17 November 1998.

· “Annealing of a crystalline ferroelectric memory cell,” S. Aggarwal, A.M.Dhote and R.Ramesh, 6274,388, 14 August 2001.

· “Bismuth ferrite films and devices grown on silicon,” R. Ramesh, 7696549, 13 April 2010.

A complete list of Ramesh’s patents is available at http://www2.lbl.gov/msd/people/investigators/ramesh_investigator.html

Awards and Honors

2014 TMS Bardeen Prize
Distinguished alumnus, Indian Institute of Science, 2012
Elected member, U.S. National Academy of Engineering, 2011
American Physical Society James McGroddy New Materials Prize, 2010
Materials Research Society Fellow, 2009
Materials Research Society David Turnbull Award, 2007
C.K. Majumdar Lectureship Award, Bose Institute, Calcutta, India Brahm Prakash Chair, Indian Institute of Science, Bangalore, India, 2006
Fellow, American Association for the Advancement of Science, 2005
American Physical Society Adler Lectureship, 2005
Distinguished University Professor, University of Maryland, College Park, 2003
Fellow, American Physical Society, 2001
Alexander von Humboldt Senior Scientist Prize, 2001

Notable publications

1. J. Wang, J.B. Neaton, H. Zheng, V. Nagarajan, S.B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D.G. Schlom, U.V. Waghmare, N.A. Spaldin, K.M. Rabe, M. Wuttig, and R. Ramesh, “Epitaxial BiFeO3 Multiferroic Thin Film Heterostructures,” Science 299, 1719 (2003).

Importance: This paper described the ferroelectric properties of the multiferroic BiFeO3 system. It started the rejuvenation of the field of multiferroics.

2. H. Zheng, J. Wang, S.E. Lofland, Z. Ma, L. Mohaddes-Ardabili, T. Zhao, L. Salamanca-Riba, S.R. Shinde, S.B. Ogale, F. Bai, D. Viehland, Y. Jia, D.G. Schlom, M. Wuttig, A. Roytburd, and R. Ramesh, “Multiferroic BaTiO3-CoFe2O4 Nanostructures,” Science 303, 661 (2004).

Importance: This paper showed how one can create a 3-D heteroepitaxial nanostructure consisting of a ferromagnetic spinel phase embedded epitaxially in a ferroelectric perovskite matrix. It also showed electric field control of magnetism.

3. T. Zhao, A. Scholl, F. Zavaliche, K. Lee, M. Barry, A. Doran, M.P. Cruz, Y.H. Chu, C. Ederer, N.A. Spaldin, R.R. Das, D.M. Kim, S.H. Baek, C.B. Eom, and R. Ramesh. Electrical control of antiferromagnetic domains in multiferroic BiFeO3 films at room temperature. Nature Materials 5, 823 (2006).

Importance: This paper described the imaging of antiferromagnetic domains in the multiferroic BiFeO3 system using xray linear dichroism coupled with photoemission electron microscopy. It also showed that when the ferroelectric domains are switched with an electric field, the antiferromagnetism also changes correspondingly.

4. F. Zavaliche, et al., “Electric field-induced magnetization switching in epitaxial columnar nanostructures”, Nanoletters 5, 1793-1796 (2005).

Importance: This paper describes the fundamental mechanisms by which the magnetic state of a ferromagnetic nanopillar can be controlled with an electric field applied to the ferroelectric matrix in which the magnet is embedded.

5. R. Ramesh and N.A. Spaldin, “ Multiferroics: progress and prospects in thin films”, Nature Materials, 6, 21(2007).

Importance: This is an invited review that summarized the advances and opportunities in multiferroic thin film materials.

6. Y.H.Chu, et al., Electric field control of ferromagnetism using a magnetoelectric multiferroic, Nature Materials, 7, 478(2008).

Importance: This paper describes an approach by which the ferromagnetic state is controlled through the application of an electric field to a multiferroic that the ferromagnet is in contact with.

7. J. Seidel, et al., “Conduction at domain walls in oxide multiferroics”, Nature Materials 8 (3): 229-234.

Importance: This paper describes a novel observation of electronic conduction at ferroelectric domain walls. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO3. The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations.

8. R.J. Zeches, et al., “A Strain-Driven Morphotropic Phase Boundary in BiFeO3.” Science 326 (5955): 977-980.

Importance: this paper is the first paper that explores the use of epitaxial strain to control the phase stability and create a nanoscale mixed phase structure in multiferroics.

9. Yang, CH, et al., “Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films”, Nature Materials 8 (6): 485-493(2009).

Importance: Here, we present the observation of an electronic conductor–insulator transition by control of band-filling in the model antiferromagnetic ferroelectric BiFeO3 through Ca doping. Application of electric field enables us to control and manipulate this electronic transition to the extent that a p–n junction can be created, erased and inverted in this material.

10. S.M. Wu, et al., “Reversible electric field control of exchange bias in a multiferroic field effect t device.” Nature Materials 9 (5955): 756-760(2010).

Importance: In this article, we demonstrated electrical control of exchange bias using a field-effect device employing multiferroic (ferroelectric/antiferromagnetic) BiFeO3 as the dielectric and ferromagnetic La0.7Sr0.3MnO3 as the conducting channel; we can reversibly switch between two distinct exchange-bias states by switching the ferroelectric polarization of BiFeO3. This is an important step towards controlling magnetization with electric fields, which may enable a new class of electrically controllable spintronic devices.

11. S.Y. Yang, et al., “Above-bandgap voltages from ferroelectric photovoltaic devices.” Nature Nanotechnology 5, 143-147(2010).

Importance: Here, we report the discovery of a fundamentally different mechanism for photovoltaic charge separation, which operates over a distance of 1–2 nm and produces voltages that are significantly higher than the bandgap. The separation happens at ferroelectric domain walls in BiFeO3. Electric-field control over domain structure allows the photovoltaic effect to be reversed in polarity or turned off.

12. Spaldin, N; Cheong, SW; Ramesh, R, Multiferroics: Past, Present, and Future Physics Today, 64, 9(2010).

Importance: This was an invited review of the field of Multiferroics and Magnetoelectrics, based on the APS McGroddy Prize.

13. Heron, J. T.; Trassin, M.; Ashraf, K.; Gajek, M.; He, Q.; Yang, S. Y.; Nikonov, D. E.; Chu, Y-H.; Salahuddin, S.; Ramesh, R., Electric-Field-Induced Magnetization Reversal in a Ferromagnet-Multiferroic Heterostructure, Physical Review Letters, 107, 217202(2011).

Importance: Here we show a nonvolatile, room temperature magnetization reversal determined by an electric field in a ferromagnet-multiferroic system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a magnetoelectric device demonstrates an avenue for next generation, low-energy consumption spintronics.

14. G. Catalan, et al., “Domain Wall Nanoelectronics.” Reviews of Modern Physics 84, 119-156(2012).

Importance: In this paper the properties of domain walls are reviewed, focusing attention on ferroelectrics and multiferroics but making comparisons where possible with magnetic domains and domain walls. This review spotlights on a new paradigm of ferroic devices where the domain walls, rather than the domains, are the active element. These include domain wall conductivity (metallic or even superconducting in bulk insulating or semiconducting oxides) and the fact that domain walls can be ferromagnetic while the surrounding domains are not.

15. S. Jin, T.H. Tiefel, M. McCormack, R.A. Fastnacht, R. Ramesh, and L.H. Chen. Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films. Science 264, 413-415 (1994).

Importance: This was the first paper to outline the large (colossal) magnetoresistance in manganites.

16. S.Matthews, R.Ramesh, T.Venkatesan and J.Benedetto, "Ferroelectric field effect transistor based on epitaxial perovskite heterostructures", Science 276, 238(1997).

Importance: This paper describes an approach to modulate the carrier density in an ultrathin La-Ca-Mn-O layer through a ferroelectric field effect.

17. J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh, and T. Venkatesan. Direct evidence for a half-metallic ferromagnet. Nature 392, 794-796 (1998).

Importance: This was the first paper that described possibility of forming a half-metallic ferromagnet in LSMO using spin polarized photoemission spectroscopy.

18. J.-H. Park, E. Vescovo, H.-J. Kim, C. Kwon, R. Ramesh, and T. Venkatesan. Magnetic properties of surface boundary of a half-metallic ferromagnet La0.7Sr0.3MnO3. Phys. Rev. Lett. 81, 1953-1956 (1998).

Importance: This paper describes the magnetic properties of the half metallic ferromagnet, LSMO.

19. R. Ramesh, A. Inam, W.K. Chan, B. Wilkens, K. Myers, K. Remschnig, D.L. Hart, and J.M. Tarascon. Epitaxial cuprate superconductor/ferroelectric heterostructures. Science 252, 944-946 (1991).

Importance: This was the first paper that described the possible use of conducting perovskites as contact electrodes for ferroelectrics. It ultimately led to the use of such electrodes to solve the fatigue and imprint problem. This is the approach that is used by industry.

20. R. Ramesh, W.K. Chan, B. Wilkens, H. Gilchrist, T. Sands, J.M. Tarascon, V.G. Keramidas, D.K. Fork, J. Lee, and A. Safari. Fatigue and retention in ferroelectric Y-Ba-Cu-O/Pb-Zr-Ti-O/Y-Ba-Cu-O heterostructures. Appl. Phys. Lett. 61, 1537-1539 (1992).

Importance: This was the first paper that described the fatigue free behavior in PZT based ferroelectrics through the use of conducting YBCO electrodes.

21. R. Ramesh, H. Gilchrist, T. Sands, V.G. Keramidas, R. Haakenaasen, and D.K. Fork. Ferroelectric La-Sr-Co-O/Pb-Zr-Ti-O/La-Sr-Co-O heterostructures on silicon via template growth. Appl. Phys. Lett. 63, 3592-3594 (1993).

Importance: This was the paper that described the fatigue free behavior in PZT based ferroelectrics through the use of conducting LSCO electrodes, grown on a Si wafer.

22. O. Auciello, J.F. Scott and R. Ramesh, “The physics of ferroelectric memories”, Physics Today, 51, 22(1998).

Importance: This was an invited review that summarized the advances and opportunities in ferroelectric thin fim materials.

23. R. Ramesh, S. Aggarwal and O. Auciello. Science and Technology of ferroelectric thin films for nonvolatile memories. Annu. Rev. Mater. Sci. 32, 191(2001).

Importance: This was an invited review that summarized the advances and opportunities in ferroelectric thin fim materials for nonvolatile memory applications.

24. Marti, X.; Fina, I.; Frontera, C.; Liu, Jian; Wadley, P.; He, Q.; Paull, R. J.; Clarkson, J. D.; Kudrnovsky, J.; Turek, I.; Kunes, J.; Yi, D.; Chu, J-H.; Nelson, C. T.; You, L.; Arenholz, E.; Salahuddin, S.; Fontcuberta, J.; Jungwirth, T.; Ramesh, R., Room-temperature antiferromagnetic memory resistor, Nature Materials, 13, 367-374(2014).

Importance: This paper reports a room-temperature bistable antiferromagnetic (AFM) memory using a resistor made of a FeRh. On cooling to room temperature, AFM order sets in with the direction of the AFM moment predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance.

25. Heron, JT , Schlom, DG , Ramesh, R, Electric field control of magnetism using BiFeO3-based heterostructures, Applied Physics Reviews Volume: 1,021303(2014).

Importance: In this article we review the advances and highlight challenges toward this goal with a particular focus on the room temperature magnetoelectric multiferroic, BiFeO3, exchange coupled to a ferromagnet. This review summarizes our understanding of the nature of exchange coupling and the mechanisms of the voltage control of ferromagnetism observed in these heterostructures.

26. Heron, JT , Bosse, JL , He, Q , Gao, Y , Trassin, M, Ye, L , Clarkson, JD, Wang, C , Liu, J , Salahuddin, S ,Ralph, DC , Schlom, DG , Iniguez, J ,Huey, BD , Ramesh, R , Deterministic switching of ferromagnetism at room temperature using an electric field, Nature,516, 370-373(2014).

Importance: The technological appeal of multiferroics is the ability to control magnetism with electric field. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching.

27. Khan, A.I., Chatterjee, K, Wang, B , Drapcho, S , You, L ,Serrao, C, Bakaul, SR, Ramesh, R , Salahuddin, S, Negative capacitance in a ferroelectric capacitor, Nature Materials 14, 182-186 (2015).

Importance: The Boltzmann distribution of electrons poses a fundamental barrier to lowering energy dissipation in conventional electronics, often termed a Boltzmann Tyranny. Negative capacitance in ferroelectric materials, which stems from the stored energy of a phase transition could provide a solution. This paper reports the observation of negative capacitance in a thin, epitaxial ferroelectric film. Analysis of this ‘inductance’-like behavior from a capacitor presents an unprecedented insight into the intrinsic energy profile of the ferroelectric material and could pave the way for completely new applications.

28. A.K. Yadav, et al, “Observation of Polar Vortices in Oxide Superlattices, Nature, accepted, November 2015.

Importance: The complex interplay of spin, charge, orbital, and lattice degrees of freedom has provided for a plethora of exotic phase and physical phenomena. In this work, we leveraged the competition between charge, orbital, and lattice degrees of freedom in superlattices of PbTiO3/SrTiO3 to produce complex, vortex-antivortex pairs (that exhibit smoothly varying ferroelectric polarization with a 10 nm periodicity) that are reminiscent of topological features such as skyrmions and merons.

Additional notable papers and a complete list of publications is available at http://www2.lbl.gov/msd/people/investigators/ramesh_investigator.html

Editorial Board Memberships

Ramesh has served on the Editorial Board of the Journal of Applied Physics, Applied Physics Letters, Integrated Ferroelectrics, Journal of Materials Research, Japanese Journal of Applied Physics and the Journal of Electroceramics.

Sources Cited

1. Ramesh, R., Chan, W. K., Wilkens, B., Gilchrist, H., Sands, T., Tarascon, J. M., ... & Safari, A. (1992). Fatigue and retention in ferroelectric Y‐Ba‐Cu‐O/Pb‐Zr‐Ti‐O/Y‐Ba‐Cu‐O heterostructures. Applied Physics Letters, 61(13), 1537-1539.

2, Ramesh, R., Gilchrist, H., Sands, T., Keramidas, V. G., Haakenaasen, R., & Fork, D. K. (1993). Ferroelectric La‐Sr‐Co‐O/Pb‐Zr‐Ti‐O/La‐Sr‐Co‐O heterostructures on silicon via template growth. Applied Physics Letters,63(26), 3592-3594.

3. Jin, S., Tiefel, T. H., McCormack, M., Fastnacht, R. A., Ramesh, R., & Chen, L. H. (1994). Thousandfold change in resistivity in magnetoresistive La-Ca-Mn-O films. Science, 264(5157), 413-415.

4. Mathews, S., Ramesh, R., Venkatesan, T., & Benedetto, J. (1997). Ferroelectric field effect transistor based on epitaxial perovskite heterostructures. Science, 276(5310), 238-240.

5. Wang, J. B. N. J., Neaton, J. B., Zheng, H., Nagarajan, V., Ogale, S. B., Liu, B., ... & Ramesh, R. (2003). Epitaxial BiFeO3 multiferroic thin film heterostructures. Science, 299(5613), 1719-1722.

6. Zheng, H., Wang, J., Lofland, S. E., Ma, Z., Mohaddes-Ardabili, L., Zhao, T., ... & Ramesh, R. (2004). Multiferroic BaTiO3-CoFe2O4 nanostructures. Science, 303(5658), 661-663

7. Zeches, R. J., Rossell, M. D., Zhang, J. X., Hatt, A. J., He, Q., Yang, C. H., ... & Ramesh, R. (2009). A strain-driven morphotropic phase boundary in BiFeO3. Science, 326(5955), 977-980.

8. Yang, S. Y., Seidel, J., Byrnes, S. J., Shafer, P., Yang, C. H., Rossell, M. D., ... & Ramesh, R. (2010). Above-bandgap voltages from ferroelectric photovoltaic devices. Nature nanotechnology, 5(2), 143-147.

9. Polking, M. J., Zheng, H., Ramesh, R., & Alivisatos, A. P. (2011). Controlled synthesis and size-dependent polarization domain structure of colloidal germanium telluride nanocrystals. Journal of the American Chemical Society,133(7), 2044-2047.

10. Heron, J. T., Bosse, J. L., He, Q., Gao, Y., Trassin, M., Ye, L., ... & Ramesh, R. (2014). Deterministic switching of ferromagnetism at room temperature using an electric field. Nature, 516(7531), 370-373.

11. Yadav, A. K., Nelson, C. T., Hsu, S. L., Hong, Z., Clarkson, J. D., Schlepüetz, C. M., ... & Ramesh, R.. (2016). Observation of polar vortices in oxide superlattices. Nature. (16416). doi:10.1038/

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