Polarization density waves in SrTiO3

by Mariano Trigo (SLAC National Accelerator Laboratory)

Tuesday 10 Sept 2024, 13:00 → 14:00 Europe/Berlin

E1.173 (European XFEL Schenefeld)

Excitation of materials with ultrafast light pulses can induce novel states of matter not accessible in thermodynamic equilibrium. Recent measurements on the quantum paraelectric SrTiO₃ showed that strong single- and multi-cycle terahertz (THz) fields can induce transient ferroelectricity (1-2), raising the prospects for ultrafast, reversible control of the material’s structure. These observations contrast strongly with equilibrium measurements that show an incipient phase with a different instability where the polarization is spatially modulated at low temperature (3–5), highlighting the need for microscopic structural information of the nonequilibrium ferroelectric state. In this talk I will present results on quantum paraelectric SrTiO₃ where we combined THz excitation with diffuse x-ray scattering, which enables probing collective excitations at nanometer lengthscales. We introduce a novel approach to probe inversion symmetry breaking that reveals hybrid polar-acoustic vibrations that are particularly soft at lengthscales of tens of nanometers. This indicates a structural instability in SrTiO₃ with spatially-modulated polarization distinct from the homogeneous ferroelectric(5,6). Our results (7) highlight the importance of probing fluctuations with momentum resolution and provide new insight into the microscopic structure of transient phases.

References

[1] X. Li, T. Qiu, J. Zhang, E. Baldini, J. Lu, A. M. Rappe, and K. A. Nelson, Science 364, 1079 (2019).

[2] T. F. Nova, A. S. Disa, M. Fechner, and A. Cavalleri, Science 364, 1075 (2019).

[3] M. J. Coak, C. R. S. Haines, C. Liu, S. E. Rowley, G. G. Lonzarich, and S. S. Saxena, Proceedings of the National Academy of Sciences 117, 12707 (2020).

[4]  S. E. Rowley, L. J. Spalek, R. P. Smith, M. P. M. Dean, M. Itoh, J. F. Scott, G. G. Lonzarich, and S. S. Saxena, Nature Physics 10, 367 (2014).

[5] G. G. Guzmán-Verri, C. H. Liang, and P. B. Littlewood, Physical Review Letters 131, 046801 (2023).

[6] B. Fauqué, P. Bourges, A. Subedi, K. Behnia, B. Baptiste, B. Roessli, T. Fennell, S. Raymond, and P. Steffens, Physical Review B 106, L140301 (2022).

[7] G. Orenstein et al, https://arxiv.org/abs/2403.17203

 

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