Abstract
Wölfle and Balatsky [Phys. Rev. B 98, 104505 (2018)2469-995010.1103/PhysRevB.98.104505] have proposed a microscopic pairing mechanism for doped SrTiO3 (STO) based on the gradient coupling of electronic density to the soft transverse optical (TO) phonon mode. Since this coupling to TO phonons is usually weak, this conclusion is surprising, especially for a low-density superconductor such as STO, where the density of states is small. A crucial step in the argument made by Wölfle and Balatsky is that the displacement vector of the TO mode is not strictly perpendicular to the momentum vector, making a deformation coupling possible. We show that they have made a mistake in computing the eigenvector and have grossly overestimated this lack of orthogonality. When corrected, the coupling is negligible. We also use transport data to put upper bounds on the coupling constant which are much smaller than the estimate by Wölfle and Balatsky. Finally, we also object to their use of the Eliashberg equation when the phonon frequency is larger than the Fermi energy.
| Original language | English |
|---|---|
| Article number | 226501 |
| Journal | Physical Review B |
| Volume | 100 |
| Issue number | 22 |
| DOIs | |
| State | Published - 20 Dec 2019 |
Bibliographical note
Publisher Copyright:© 2019 American Physical Society.
Funding
We thank Peter Wölfle for pointing out Ref. [11] . J.R. acknowledges work to appear with Zhen Bi and Vladyslav Kozii which is closely related to some of the results presented here. P.A.L. acknowledges the support of DOE under Grant No. FG02-03-ER46076. J.R. acknowledges funding by the Israeli Science Foundation under grant No. 967/19.
| Funders | Funder number |
|---|---|
| Israeli Science Foundation | 967/19 |
| U.S. Department of Energy |