Sara Callori successfully defended her PhD thesis today. She will soon start a postdoc in Sydney, Australia. Congratulations to Sara on an excellent thesis and for setting the current group record for champagne at PhD defense (5 bottles..)!
Field-Dependent Domain Distortion and Interlayer Polarization Distribution in PbTiO3/SrTiO3 Superlattices
P. Chen, M.P. Cosgriff, Q. Zhang, S.J. Callori, B.W. Adams, E.M. Dufresne, M. Dawber, and P.G. Evans
Phys. Rev. Lett. 110, 047601 (2013).
Congratulations to Kevin who today was named as a finalist in the Intel Science Talent Search for the work he did in our group this summer!
Both Grace Pan and Kevin Chen were today named as semifinalists in the Intel Science Talent Search for the work they did in our group over the summer. Congratulations to them both, and thanks to Sara and John who helped them get started with their projects!
John Sinsheimer defended his thesis today to become the first PhD graduate from our group. John will start as a postdoc at Brookhaven National Laboratory in January. Congratulations to John on his excellent thesis!
Congratulations to Grace Pan who was named a Siemens semifinalist today for the work she did with us this summer!
Engineering polarization rotation in a ferroelectric superlattice
J. Sinsheimer, S.J. Callori, B. Bein, Y. Benkara, J. Daley, J. Coraor, D. Su, P.W. Stephens, and M. Dawber
Phys. Rev. Lett 109, 167601 (2012).
A key property that drives research in ferroelectric perovskite oxides is their strong piezoelectric response in which an electric field is induced by an applied strain, and vice-versa for the converse piezoelectric effect. We have achieved an experimental enhancement of the piezoelectric response and dielectric tunability in artificially layered epitaxial PbTiO3/CaTiO3 superlattices through an engineered rotation of the polarization direction. As the relative layer thicknesses within the superlattice were changed from sample to sample we found evidence for polarization rotation in multiple x-ray diffraction measurements. Associated changes in functional properties were seen in electrical measurements and piezoforce microscopy. The results demonstrate a new approach to inducing polarization rotation under ambient conditions in an artificially layered thin film.
This paper is also available on the arXiv at http://arxiv.org/abs/1209.3227.
Grace and Kevin both presented excellent posters at the closing ceremony of this year's Simons program. We will miss them both!
Ferroelectric PbTiO3/SrRuO3 superlattices with broken inversion symmetry
S.J. Callori, J. Gabel, D. Su, J. Sinsheimer, M.V. Fernandez-Serra, M. Dawber
Phys. Rev. Lett. 109, 067601 (2012)
Lukas Kuerten has successfully defended his Master's thesis on “Observation of natural domain structure in ferroelectric superlattices by Piezoresponse Force Microscopy”. Look out for a preprint on this topic soon!
Our paper on PTO/SRO superlattices has been accepted for publication in Physical Review Letters!
Matt has written a viewpoint in Physics on the interesting discovery of a material in which electronic ferroelectricity is opposed to, and overpowers, ionic ferroelectricity.
The viewpoint can be found here and the Phys. Rev. Lett. paper it describes can be found here.
Juli Coraor has been named as a finalist in the Intel Science Talent Search and will go to Washington DC in March to compete with the top 40 students from the nearly 2000 who entered. Congratulations to Juli!
Ferroelectric PbTiO3/SrRuO3 superlattices with broken inversion symmetry
S.J. Callori, J. Gabel, D. Su, J. Sinsheimer, M.V. Fernandez-Serra, M. Dawber
We have fabricated PbTiO3/SrRuO3 superlattices with ultra-thin SrRuO3 layers. Due to the superlattice geometry, the samples show a large anisotropy in their electrical resistivity, which can be controlled by changing the thickness of the PbTiO3 layers. Therefore, along the ferroelectric direction, SrRuO3 layers can act as dielectric, rather than metallic, elements. We show that, by reducing the concentration of PbTiO3, an increasingly important effect of polarization asymmetry due to compositional inversion symmetry breaking occurs. The results are significant as they represent a new class of ferroelectric superlattices, with a rich and complex phase diagram. By expanding our set of materials we are able to introduce new behaviors that can only occur when one of the materials is not a perovskite titanate. Here, compositional inversion symmetry breaking in bi-color superlattices, due to the combined variation of A and B site ions within the superlattice, is demonstrated using a combination of experimental measurements and first principles density functional theory.
A preprint of this paper is available on the arXiv at http://arxiv.org/abs/1201.2893
Congratulations to Juli Coraor for being named as a semifinalist in both the Intel and Siemens Science competitions! Juli is a high school senior at Huntington High School. She was a Simons Summer Research fellow in the summer of 2011 and continues to be actively involved with our group.