Journal Article

FZJ-2024-06537

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Transition to metallic and superconducting states induced by thermalor electrical deoxidation of the dislocation network in the surface regionof SrTiO3

Szot, K. ; Rodenbücher, C. (Corresponding author)FZJ* ; Rogacki, K. ; Bihlmayer, G.FZJ* ; Speier, W.FZJ* ; Roleder, K. ; Krok, F. ; Keller, H. ; Simon, A. ; Bussmann-Holder, A.

2024
MDPI Basel

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Please use a persistent id in citations: doi:10.3390/nano14231944  doi:10.34734/FZJ-2024-06537

Abstract: The question as to why deoxidized SrTiO3−δ becomes metallic and superconducting at extremely low levels of oxygen vacancy concentration has been a mystery for many decades. Here, we show that the real amount of effused oxygen during thermal reduction, which is needed to induce superconducting properties, is in the range of only 1014/cm3 and thus even lower than the critical carrier concentrations assumed previously (1017–1019/cm3). By performing detailed investigations of the optical and electrical properties down to the nanoscale, we reveal that filaments are forming during reduction along a network of dislocations in the surface layer. Hence, a reduced epi-polished SrTiO3−δ crystal has to be regarded as a nano-composite consisting of a perfect dielectric matrix with negligible carrier density, which is short-circuited by metallic filaments with a local carrier density in the range of 1020/cm3. We present that electro-degradation leads to a more pronounced evolution of filamentary bundles and thus can generate a superconducting state with higher TC than thermal reduction. These findings indicate that traditional homogeneous models of superconductivity in self-doped SrTiO3−δ need to be revised, and we propose an alternative explanation taking into account the coexistence of metallic dislocation cores with polar insulating regions allowing for polaronic coupling.

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Contributing Institute(s):

1. Elektrochemische Verfahrenstechnik (IET-4)
2. Quanten-Theorie der Materialien (PGI-1)
3. Science Office (PGI-SO)

Research Program(s):

1. 5211 - Topological Matter (POF4-521) (POF4-521)
2. DFG project G:(GEPRIS)491111487 - Open-Access-Publikationskosten / 2025 - 2027 / Forschungszentrum Jülich (OAPKFZJ) (491111487) (491111487)
3. 1231 - Electrochemistry for Hydrogen (POF4-123) (POF4-123)

Appears in the scientific report 2024

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