LPTMC Seminars

Superconducting dome and incipient modulate phase in SrTiO3

SrTiO₃ 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 SrTiO₃ 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 c₄₄), with this coupling being most pronounced at small q-vectors. I will further show that SrTiO₃ 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 SrTiO₃ 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 SrTiO₃. This will provide further evidence of TO–TA hybridization in SrTiO₃.