LMI Seminar: Structural states of optically driven SrTiO3

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Abstract:

Shaping crystal structures and altering their properties utilizing optical pulses has become a unique approach in ultrafast science. But how versatile is this approach, and how many of these states possibly exist in a single material? Here I will examine this question for SrTiO3, a prototypical perovskite material.

Illuminating SrTiO3 with optical pulses covering wavelengths ranging from 4 meV to 4 eV produces distinctive non-equilibrium states [1–4]. For example, optical pulses in the low-frequency range (4meV-100 meV) create a short-lived polar ordering, metastable ferroelectricity, or antiferrodistortive ordering. In contrast, pulses tuned to the frequency of the eV range results in a suppression of these orders.

I will show how this diverse and rich behavior originates from the initial optical excitations processes involving lattice or electronic degrees of freedom and their interplay. Utilizing the results of first-principle calculations, I will show that although the interaction of lattice, electronic degrees, and fluctuations is the same, the non-linear processes launched by the optical pulses result in different final states. To support this discussion, I will compare these theory results with the experimental findings of ultrafast X-ray and spectroscopic investigations. Finally, I will discuss how these findings for SrTiO3 apply to other materials.

References:

1. Kozina, M. et al. Terahertz-driven phonon upconversion in SrTiO3. Nat Phys 15, 387–392 (2019).

2. Li, X. et al. Terahertz field–induced ferroelectricity in quantum paraelectric SrTiO3. Science 364,   1079–1082 (2019).

3. Nova, T. F., Disa, A. S., Fechner, M. & Cavalleri, A. Metastable ferroelectricity in optically strained SrTiO3. Science 364, 1075–1079 (2019).

4. Porer, M. et al. Ultrafast Relaxation Dynamics of the Antiferrodistortive Phase in Ca Doped SrTiO3. Phys Rev Lett 121, 055701 (2018).