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arXiv · 2203.15495

Mesoscopic tunneling in strontium titanate

Benoît Fauqué·Philippe Bourges·Alaska Subedi·Kamran Behnia·Benoît Baptiste·Bertrand Roessli·Tom Fennell·Stéphane Raymond·Paul Steffens
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Abstract

Spatial correlation between atoms can generate a depletion in the energy dispersion of acoustic phonons. Two well known examples are rotons in superfluid helium and the Kohn anomaly in metals. Here we report on the observation of a large softening of the transverse acoustic mode in quantum paraelectric SrTiO$_3$ by means of inelastic neutron scattering. In contrast to other known cases, this softening occurs at a tiny wave vector implying spatial correlation extending over a distance as long as 40 lattice parameters. We attribute this to the formation of mesoscopic fluctuating domains due to the coupling between local strain and quantum ferroelectric fluctuations. Thus, a hallmark of the ground state of insulating SrTiO$_3$ is the emergence of hybridized optical-acoustic phonons. Mesoscopic fluctuating domains play a role in quantum tunneling, which impedes the emergence of a finite macroscopic polarisation.

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Benoît Fauqué, Philippe Bourges, Alaska Subedi, Kamran Behnia, Benoît Baptiste, Bertrand Roessli, Tom Fennell, Stéphane Raymond, Paul Steffens. 2022-03-29. Mesoscopic tunneling in strontium titanate. https://doi.org/10.1103/physrevb.106.l140301

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