Ideal Soft Mode-Type Quantum Phase Transition and Phase Coexistence at Quantum Critical Point inO18-ExchangedSrTiO3

Abstract

The quantum ferroelectric phase transition of 18O-exchanged SrTiO3 (x% exchanged SrTiO3 is abbreviated as STO18-x) was investigated by Raman scattering as a function of x. The result indicates the ideal soft mode-type quantum ferroelectric phase transition of STO18-x, where the 18O exchange enhances the softening of the soft mode by the suppression of quantum fluctuation. In the vicinity of the quantum critical point (x approximately xc=33%), the system results in the ferroelectric-paraelectric phase coexistence state, in clear contrast to the homogeneous ferroelectric phase in STO18-x, whose x is sufficiently larger than xc. Simultaneously, the softening of the soft mode becomes strongly rounded with the underdamped oscillation. The present result indicates that the sensitivity of the soft phonon vibration to the mass disorder is dramatically enhanced in the vicinity of the quantum critical point.

Interface Ferroelectric Transition near the Gap-Opening Temperature in a Single-Unit-Cell FeSe Film Grown on Nb-DopedSrTiO3Substrate

“…This optical phonon mode is known as the ferroelectric soft mode, which is Raman inactive, but appears in the Raman spectrum due to breaking of the inversion symmetry. [9,10,[13][14][15][16] The same Raman anomaly is also observed in 0.5 wt% Nb-doped bare NbSTO (i.e. without the FeSe film).…”

“…(We note that the mean-field FE temperature for pure STO is 37 K [19] while it is also sensitive to local inversion symmetry perturbation. [16,23]. )…”

The polarizability model for ferroelectricity in perovskite oxides

“…This observation can be explained by the fact that polarizability effects are less pronounced in this system as compared to SrTiO 3 which is evidenced by the shallower and broader double-well potential (figure 6). 3 has been investigated experimentally [155] and theoretically [154]. This was motivated by the fact that controversial results for the dynamics of the end members (x=0., x=1.)…”

Soft-mode Dynamics in the Ferroelectric Phase Transition of Quantum Paraelectric SrTiO3

“…The light scattering method is adequate for the dynamical study of the phase transition because it detects the spectra of the lattice modes as a function of both frequency and wave vector near the point in the Brillouin zone. The purpose of the present paper is to review the recent light scattering studies on the dynamical property of the oxygen-isotope induced ferroelectric phase transition in STO18 including the partially substituted ones [14][15][16][17][18][19]. The experiments are described briefly in next section, and the present experimental results in the following section are compared with the other previous experimental results in the final section.…”