Speaker
Description
Recently, superconductivity in strontium titanate and at the SrTiO3-LaAlO3 interface became a subject of renewed interest because of specific properties of SrTiO3. The superconducting phase transition in these systems occurs at very low temperatures combined with low carrier densities. Strontium titanate is a strongly polar crystal where the Fröhlich electron – LO-phonon interaction dominates in the electron response [1]. Therefore we suggest that the same interaction provides superconductivity in these systems.
Superconductivity in bulk strontium titanate and at the SrTiO3-LaAlO3 interface is analyzed discussing different approaches and paradigms. Because the LO-phonon frequencies are high with respect to both the thermal energy and the Fermi energy, the superconducting system is strongly non-adiabatic. The dielectric function method [2, 3] is shown to be the most consistent for non-adiabatic electron-phonon systems.
We have applied the dielectric function method to treat superconductivity at the SrTiO3-LaAlO3 interface [4] and in bulk doped strontium titanate using recent results for the band structure of SrTiO3 [5]. The critical temperatures are calculated without fitting. The obtained critical temperatures are in line with experimental data. The present method explains the observed multi-dome shape of the critical temperature in bulk strontium titanate as a function of the electron concentration due to multiband superconductivity.
This research was supported by the Flemish Research Foundation (FWO-Vl), project nrs. G.0115.12N, G.0119.12N, G.0122.12N, G.0429.15N, by the Scientific Research Network of the Research Foundation-Flanders, WO.033.09N, and by the Research Fund of the University of Antwerp.
References
J. T. Devreese, S. N. Klimin, J. L. M. van Mechelen, and D. van der Marel, Phys. Rev. B 81, 125119 (2010).
D. A. Kirzhnits, E. G. Maksimov, and D. I. Khomskii, J. Low Temp. Phys. 10, 79 (1973).
Y. Takada, J. Phys. Soc. Jpn. 45, 786 (1978); 49, 1267 (1980).
S. N. Klimin, J. Tempere, J. T. Devreese and D. van der Marel, Phys. Rev. B 89, 184514 (2014).
J. L. M. van Mechelen, D. van der Marel, C. Grimaldi, A. B. Kuzmenko, N. P. Armitage, N. Reyren, H. Hagemann, and I. I. Mazin, Phys. Rev. Lett. 100, 226403 (2008).
