Quantum Ferroelectric Instabilities in Superconducting ${\mathrm{SrTiO}}_3$

Journal Article · Mon Oct 01 04:00:00 EDT 2018 · Physical Review Materials

DOI:https://doi.org/10.1103/PhysRevMaterials.2.104804· OSTI ID:1490097

Arce-Gamboa, J. R.; Guzmán-Verri, G. G.

We examine the effects of strain and cation substitution on the superconducting phase of polar semiconductors near a ferroelectric quantum phase transition with a model that combines a strong coupling theory of superconductors with a standard microscopic framework for displacive polar modes coupled to strain degrees of freedom. Our calculations reveal that the superconducting transition temperature T-c is enhanced by proximity to the ferroelectric instability from the disordered side, while it is generally suppressed in the ordered phase due to its increase in dielectric stiffness and a reduction of critical fluctuations from dipolar induced anisotropies. The condensation of the pairing phonon excitations generates a kink in T-c at a charge density that is generally lower than that of the quantum critical point (QCP) and where both superconducting and ferroelectric orders set in. We apply our model to SrTiO₃ and find that the antiadiabatic limit places the kink nearly at its QCP. As the QCP is pushed to higher charge densities with either tuning parameter, we find that the dome narrows and sharpens. Our model is in qualitative and fair quantitative agreement with the recent observation of overlapping ferroelectric-like and superconducting instabilities in n-doped Sr_1-xCa_xTiO₃ and strain tuning of T-c in n-doped SrTiO₃. We compare our results to previous models invoking order-disorder lattice dynamics to describe the pairing excitations.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1490097
• Journal Information: Physical Review Materials, Journal Name: Physical Review Materials Journal Issue: 10 Vol. 2; ISSN PRMHAR; ISSN 2475-9953
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English