Glass-like Interacting Off-Centre Ca ^{+ +} Dipoles as Probes of the “Coherent Quantum State” in SrTiO ₃

Abstract

Anomalies in both the linear and the non-linear dielectric permittivity of weakly doped Srl-zCa,TiOs (z = 0.002) and strongly rising dielectric loss in the low-frequency regime evidence coupling of Ca+ + centred polar nanoregions with the predicted coherent quantum state of the host lattice. Glassiness of the nanoregion system is modelled by Lacroix-BBnktype polydispersivity with an extrapolated freezing temperature Tg = 4 K.

Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities inSr1−xCaxTiO3−Lima1, Luz2, Oliveira3 et al. 2015Phys. Rev. B323430View full textAdd to dashboardCite

“…The temperature dependent permittivities in this concentration range of Sr 1−x Ca x TiO 3 seem to extrapolate to a finite value for T ≈ 0, denoting the influence of quantum fluctuations. Therefore, these materials are referred to as quantum ferroelectrics [20,32].…”

“…These loss features can be understood by the formation of polar nanoregions seeded by the electric dipoles of off-center calcium sites embedded in the highly polarizable STO lattice. Even if these clusters remain disordered at low Caconcentrations they may experience glass-like freezing at low temperatures [32] or they may give rise to additional loss at higher temperatures due to interaction with eventually polar structural domain walls arising below the tetragonal phase transition [6,33].…”

A combined X-ray diffraction and Raman scattering study of the phase transitions in Sr1−xCaxTiO3 (x=0.04, 0.06, and 0.12)

“…Quantum fluctuations, however, preclude the condensation of this soft mode below 4 K as a result of which the dielectric constant shows saturation below 4 K [1]. SrTiO 3 is therefore termed as an incipient ferroelectric down to T % 0 K. There is also the possibility [4][5][6][7][8] of a quantum phase transition into a coherent quantum state below 36 K similar to that in liquid He II [9].…”

Relaxational dynamics of polar nanodomains in Sr 1 − x Ca x TiO 3 x = 0.002

“…It forms mesoscopic dipolar clusters due to the interaction of off-center Ca 2+ dipoles with the highly polarizable SrTiO 3 matrix [11]. Their polydispersive dielectric response [12] is empirically described by negatively skewed distribution functions of the relaxation times [13]. Extending the measurements to low frequencies, f ≥ 10 −3 Hz, and low temperatures, T ≥ 1.5 K, we are able to evidence Dixon-Nagel scaling properties [8], which clearly hint at power law decay in the time domain [7].…”