SCIENTIFIC HIGHLIGHTS

Ferroelastic domains in motion under electric fields

Optical imaging and first-principles modeling unveil the physics of domain motion driven by electric fields in ferroelastic SrTiO3 crystals

By altering the chemical composition of SrTIO3 or by straining the crystals, a remarkable wide scope of physical phenomena emerge, including superconductivity, ferroelectricity, 2D-transport or magnetism. This notable versatility makes of SrTiO3 a paradigmatic material of oxide electronics. Another fundamental feature of SrTiO3 is the transition from a cubic to a tetragonal low-temperature phase, whereby ferroelastic domains form in the crystals. There is also evidence that electric polarity emerges at domain walls, which is, a priori, an unexpected outcome, as the material itself is not polar.

Given these considerations, a natural question arises about how electric fields interact with ferroelastic domains and, in particular, whether the polar character of domain walls drives the motion of ferroelastic domains or if, on the contrary, the dielectric properties of SrTiO3 prevail on the dynamics of domains. To answer this question, we imaged the evolution of ferroelastic domains in situ (Figure), carefully controlling the orientation of the applied fields with respect to the orientation axis of the domains. By combining in-situ imaging with numerical modeling based on first-principles density-functional theory, we conclude that it is the dielectric anisotropy of tetragonal SrTiO3, rather than the intrinsic domain wall polarity, what drives the motion of the ferroelastic twins. The underlying mechanism relies on the excitation of a particular IR-active lattice mode below the tetragonal transition, which we predict to be a general characteristic of perovskites.

Authors:
Blai Casals,1 Andrea Schiaffino,1 Arianna Casiraghi,2 Sampo J. Hämäläinen,2 Diego López González,2 Sebastiaan van Dijken,2 Massimiliano Stengel,1,3 Gervasi Herranz1

Affiliation:
1Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Spain
2NanoSpin, Department of Applied Physics, Aalto University School of Science, Finland
3ICREA–Institució Catalana de Recerca i Estudis Avançats, Spain

Publication:
Low-Temperature Dielectric Anisotropy Driven by an Antiferroelectric Mode in SrTiO3
Physical Review Letters 120, 217601 (2018)
DOI: 10.1103/PhysRevLett.120.217601

Figure:
(a) Map of ferroelastic domains obtained by magneto-optical imaging. The images show the presence of {a1, a2} and {a,c} ferroelastic twins, revealed by imprinting of ferroelastic domains into a magnetostrictive film on top of SrTiO3. Micromagnetic simulations of the magnetic state shown in (b) are in agreement with the spatial distribution of magnetic domains imprinted on the magnetostrictive film (shown in (c) and (d) by the underlying ferroelastic twins in SrTiO3

Acknowledgments

This work was supported by the Spanish MAT2017-85232-R, MAT2014-56063-C2-1-R,MAT2016-77100-C2-2-P, FIS2013-48668-C2-2-P, Severo Ochoa SEV-2015-0496 grant, the Generalitat de Catalunya (2014 SGR734, 2014 SGR301), and the Väisälä foundation. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreements No. 724529 and No. 307502). Calculations were performed at Supercomputing Center of Galicia (CESGA).
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