The dielectric constants ${\epsilon }_{〈110〉}$ and their change with uniaxial $〈1\overline{1}0〉$ stress in monodomain $〈001〉$SrTi${\mathrm{O}}_3$ samples have been measured as a function of temperature. Between 4 K and 0.3 K these quantities are independent of temperature. In one sample $\epsilon \mathrm{}\left(T\right)\mathrm{}$ was measured to 0.035 K and found to be constant. This proves the quantum-mechanical stabilization of the paraelectric phase below 4 K with a very high dielectric constant $\epsilon$. The crossover from classical to quantum behavior on lowering the temperature is discussed, and it is shown that the coupling of the ferroelectric mode to acoustic ones is important. The $\epsilon \mathrm{}\left(T\right)\mathrm{}$ dependence is compared to earlier and recent theories. The former, yielding a coth ($\frac{\hslash \Omega }{\mathrm{kT}}$) term, are found to be inadequate for the crossover region. A recent biquadratic ferroelectric mode-coupling theory fits the data better.

• Received 19 July 1976

DOI:https://doi.org/10.1103/PhysRevB.19.3593

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Physical Review B 50^th Anniversary Milestones

These Milestone studies represent lasting contributions to physics by way of reporting significant discoveries, initiating new areas of research, or substantially enhancing the conceptual tools for making progress in the burgeoning field of condensed matter physics.