Raymond Walter

Microscopic origins of the large piezoelectricity of leadfree (Ba,Ca)(Zr,Ti)O 3

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses constitutes an important current scientific goal. As such, the recent discovery of a large electromechanical conversion near room temperature in (1−x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 compounds has directed attention to understanding its origin. Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically promising material. We find that its high piezoelectricity originates from the existence of large fluctuations of polarization in the orthorhombic state arising from the combination of a flat free-energy landscape, a fragmented local structure, and the narrow temperature window around room temperature at which this orthorhombic phase is the equilibrium state. In addition to deepening the current knowledge on piezoelectricity, these findings have the potential to guide the design of other lead-free materials with large electromechanical responses.

Natural optical activity and its control by electric field in electrotoroidic systems

This work is financially supported by ONR Grants No. N00014-11-1-0384, No. 00014-12-1-1034, and No. N00014-08-1-0915 (S.P. and L.B., for contributing to analytical derivations and phenomenology), ARO Grant No. W911NF-12-1- 0085 (Z.G. and L.B. for atomistic simulations under ac fields), and NSF Grant No. DMR-1066158 (L.L., R.W., and L.B for some effective Hamiltonian computations). I.S. acknowledges support from Grant No. MAT2012-33720 from the Spanish Ministerio de Economia y Competitividad. S.P. appreciates Grant No. 12-08-00887-a from the Russian Foundation for Basic Research. L.B. also acknowledges discussions with scientists sponsored by the Department of Energy, Office of Basic Energy Sciences, under Contract No. ER-46612, Javier Junquera, Pablo Aguado-Puente, and Surendra Singh.

Construction of Arbitrary Order Conformally Invariant Operators in Higher Spin Spaces

This paper completes the construction of arbitrary order conformally invariant differential operators in higher spin spaces. Jan Slovák has classified all conformally invariant differential operators on locally conformally flat manifolds. We complete his results in higher spin theory in Euclidean space by giving explicit expressions for arbitrary order conformally invariant differential operators, where by conformally invariant we mean equivariant with respect to the conformal group of

Corrigendum: Microscopic origins of the large piezoelectricity of leadfree (Ba,Ca)(Zr,Ti)O 3

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Higher Order Fermionic and Bosonic Operators on Cylinders and Hopf Manifolds

Sm acting in Euclidean space

Third order fermionic and fourth order bosonic operators

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