Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities in Sr1−xCaxTiO3−δ

B. S. de Lima; M. S. da Luz; F. S. Oliveira; L. M. S. Alves; C. A. M. dos Santos; F. Jomard; Y. Sidis; P. Bourges; S. Harms; C. P. Grams; J. Hemberger; X. Lin; B. Fauqué; K. Behnia

doi:10.1103/PhysRevB.91.045108

Interplay between antiferrodistortive, ferroelectric, and superconducting instabilities in Sr1−xCaxTiO3−δ

B. S. de Lima, M. S. da Luz, F. S. Oliveira, L. M. S. Alves, C. A. M. dos Santos, F. Jomard, Y. Sidis, P. Bourges, S. Harms, C. P. Grams, J. Hemberger, X. Lin, B. Fauqué, K. Behnia

DOI 10.1103/PhysRevB.91.045108 · Physical Review B

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Abstract

SrTiO3 undergoes a cubic-to-tetragonal phase transition at 105 K. This antiferrodistortive transition is believed to be in competition with incipient ferroelectricity. Substituting strontium by isovalent calcium induces a ferroelectric order. Introducing mobile electrons to the system by chemical nonisovalent doping, on the other hand, leads to the emergence of a dilute metal with a superconducting ground state. The link between superconductivity and the other two instabilities is a question gathering momentum in the context of a popular paradigm linking unconventional superconductors and quantum critical points. We present a set of specific-heat, neutron-scattering, dielectric-permittivity, and polarization measurements on Sr1−xCaxTiO3 (0<x<0.009) and a study of low-temperature electric conductivity in Sr0.9978Ca0.0022TiO3−δ. Calcium substitution was found to enhance the transition temperature for both antiferrodistortive and ferroelectric transitions. Moreover, we find that Sr0.9978Ca0.0022TiO3−δ has a superconducting ground state. The critical temperature in this rare case of a superconductor with a ferroelectric parent is slightly lower than in SrTiO3−δ of comparable carrier concentration. A three-dimensional phase diagram for Sr1−xCaxTiO3−δ tracking the three transition temperatures as a function of x and δ results from this study, in which ferroelectric and superconducting ground states are not immediate neighbors.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Sr0.9978Ca0.0022TiO3-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
SrTiO3-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown