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Résumé |
SrTiO_3; is a “quantum paraelectric” in which dipolar fluctuations grow upon cooling, yet long-range
ferroelectric order never develops. In this seminar, I will discuss the evolution of these dipolar fluctuations,
as measured by inelastic neutron scattering, as the system is tuned toward superconducting and
ferroelectric phases.
First, I will show that the superconducting dome of SrTiO_3 is driven by the competition between
the
increase in the density of states and the inevitable collapse of the quantum paraelectric phase under
electron doping. Second, I will demonstrate that these dipolar fluctuations couple to a transverse acoustic
mode (elastic constant c_44), with this coupling being most pronounced at small q-vectors. I will further
show that SrTiO_3; lies near a modulated phase, as evidenced by significant softening of its transverse
acoustic branch.
Both the amplitude of the coupling and the modulation vector are strongly influenced by the enhancement
of the ferroelectric and antiferrodistortive (AFD) phase transitions. These findings suggest that SrTiO_3 is
not only an incipient ferroelectric but also an incipient modulated material, with the modulated phase
cooperating, rather than competing, with ferroelectricity and the AFD transition.
If time permits, I will also present the electric-field dependence of the thermal conductivity—another
probe of acoustic phonons—in SrTiO_3. This will provide further evidence of TO–TA hybridization in
SrTiO_3. |
