Abstract
Doped SrTiO3 becomes a metal at extremely low doping concentrations n and is even superconducting at n < 1020 cm−3, with the superconducting transition temperature adopting a dome-like shape with increasing carrier concentration. In this paper it is shown within the polarizability model and from first principles calculations that up to a well-defined carrier concentration nc transverse optic mode softening takes place together with polar nano-domain formation, which provides evidence of inhomogeneity and a two-component type behavior with metallicity coexisting with polarity. Beyond this region, a conventional metal is formed where superconductivity as well as mode softening is absent. For n ≤ nc the effective electron-phonon coupling follows the superconducting transition temperature. Effusion measurements, as well as macroscopic and nanoscopic conductivity measurements, indicate that the distribution of oxygen vacancies is local and inhomogeneous, from which it is concluded that metallicity stems from filaments which are embedded in a polar matrix as long as n ≤ nc.
Highlights
SrTiO3 (STO) is one of the best investigated systems for scientific and technological reasons.Early on, research activities focused on the cubic to tetragonal phase transition at TS = 105 K [1,2,3,4,5,6]and the transverse optic mode softening suggesting a polar instability [7,8,9,10]
Upon replacing Sr by Ca or La, or Ti with Nb, or removing oxygen, superconductivity has been observed at low temperature with a dome-like dependence of the transition temperature upon doping [17,18,19,20,21,22,23,24,25]
The metallic state of STO and its metal / insulator (M/I) transition have attracted intense attention, since metallicity is observed at a carrier concentration which reaches a critical value defined by the Mott’s criterion [35]
Summary
SrTiO3 (STO) is one of the best investigated systems for scientific and technological reasons. The metallic state of STO and its metal / insulator (M/I) transition have attracted intense attention, since metallicity is observed at a carrier concentration which reaches a critical value defined by the Mott’s criterion [35] This transition can be induced through a reduction in high temperatures and under low oxygen partial pressure, e.g., in a vacuum, Ti-getter, or H2 atmosphere [18,36]. Effusion measurements and macroscopic and nanoscopic conductivity measurements show that the removal of only 1013 –1014 oxygen ions/cm turns STO into a metallic state [37,38], and violate the Mott criterion Such an extremely low distribution of oxygen vacancies gives rise to local inhomogeneity, which implies that the reduction process is of local character and takes place only near the core of dislocations [37,38,39]. These results are supported by an experimental conductivity study which provides evidence that the filamentary character of the conductivity is in coexistence with polar nano-domains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
