Strain Induced Multifunctionality in Complex Oxides

1. Strain Induced Multifunctionality in Complex Oxides Antiferrodistortive transition Ferroelectric transition Venkatraman Gopalan, Pennsylvania State University,DMR-0512165 • Multifunctional electronic complex oxideswith coexisting properties such as polarization, magnetization, and strain states are attracting significant interest due to the possibility of a rich array of coupled phenomena that allow tuning of these properties, or even inducing new properties with electric field, magnetic field or strain. Recent work by our collaborator (J.H. Haeni, D. G. Schlom et al., Nature 430, 758 (2004)) has shown that SrTiO3 which is not a ferroelectric in bulk form, can be made ferroelectricby strained growth in thin film form. We have made further key advances: • First direct imaging of ferroelectric domains (Fig. (a)) and domain switching under electric fields (Fig. (b)) in strained SrTiO3 by Piezoelectric Force Microscopy. Comparison with phase-field simulations (Fig.(c) and (d)) indicates 90 domain wall motion. (Y. L. Li, et al. Phys. Rev. B, 73, 184112 (2006); A. Vasudevarao et al., Phys. Rev. B., accepted (2006)). • First probing of multiferroicity: Strain not only induces ferroelectricity, but also induces multiferroicity, that is, the coexistence of both ferroelectric and ferroelastic domains in SrTiO3. Unlike other ferroelectrics, the ferroelectric polarization (p, which is a polar property) and antiferroelastic rotation of oxygen cages (denoted by q, which is an axial property) are independent, and give rise to two transitions (Fig. (e) measured using nonlinear optical probing). • Significance: From a symmetry perspective, strained SrTiO3 has striking resemblance to multiferroics such as BiFeO3 that exhibit coexistence of ferroelectricity (p) and antiferromagnetism (q), that may allow electric control of magnetism. By dynamically straining complex oxides, new properties can be induced and tuned in materials, leading to a vast array of tunable ferroelectric, piezoelectric, pyroelectric, and optical devices. (a) (b) 10mm E= 1kV/mm (c) (d) p p (e)

2. (a) (d) (b) (e) (c) The Science and Technology of Light: Workshop for High School Girls Venkatraman Gopalan, Pennsylvania State University, DMR-0512165 The Science and Technology of Light: Douglass Science Camp for High School Girls: A workshop (panels (a)-(d)) was organized by Gopalan, at Rutgers university in March 2006 (In conjunction with Prof. Darrell Schlom (PI, NSF-NIRT)). 48 of the top high school girls interested in science from across New Jersey attended this one day event. Gopalan conducted the workshop for 6 groups of 8 girls each. The response was enormously positive. See Art from an attendee (right panel (b)): “I Love Science”. The scribble relates to the measurement we made that the velocity of light in a glass fiber was 1.5 times slower than in air. The refractive index of glass was therefore deduced to be 1.5. Women in Science and Engineering (WISE) High School Girls Camp at Penn State: This event was held in June 2006, and presented the above-mentioned optical voice link module to visiting high school girls. Two graduate students from Gopalan group, Eftihia Vlahos and Lili Tian conducted this workshop. Two high school teachers in Pennsylvania, Paul Longwell from Hollidaysburg, PA (see panel (e)), working with graduate student, Lili Tian on electro-optic measurements) and Wendy McCoullough from State College, PA spent time in Gopalan group in summer (2005) to develop teaching curricula in optics and lasers to take back to their classes in Fall. Faculty from Undergraduate Institution : David McGee from Drew University spent time in PIs lab (July 2006), learning prism coupling in optical waveguides. The PIs group shared the home-built design of the coupler with David, who is reproducing it in Drew University for purposes of undergraduate education and research.