Low-temperature dynamics of the quantum critical soft-phonon mode in SrTiO3
SrTiO3 (STO) forms the textbook example of a quantum paraelectric and of a quantum critical ferroelectric system ¿ it naturally lies very close to a quantum critical point (QCP) where long-range ferroelectric order is suppressed to zero temperature. The relevant physics of STO are dictated only by the phonons ¿ making it an extremely clean model system, and the behaviour of the soft optical mode which would give rise to ferroelectricity has previously been characterised by inelastic neutron experiments down to 4.5 K. Our recent dielectric measurements show that below 2 K, the inverse dielectric susceptibility displays an unexpected upturn which is attributed to the coupling of the soft optical mode with another acoustic phonon. This theoretical coupling of these phonon modes remains to be directly explored by inelastic neutron scattering below the temperature of this new dielectric behaviour. We propose to perform an inelastic scattering measurement using IN8 to measure the optical and acoustic mode in STO down to 50 mK. Direct observation of these phonon modes is necessary for developing this theory, which will impact also on the observation of superconductivity in doped STO.
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David M Jarvis; M.J. Coak; Shiyu Deng; C R S Haines; IVANOV Alexandre; LIU Cheng; PIOVANO Andrea; SAXENA Siddharth and WILDES Andrew. (2021). Low-temperature dynamics of the quantum critical soft-phonon mode in SrTiO3. Institut Laue-Langevin (ILL) doi:10.5291/ILL-DATA.7-02-212
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