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Critical Doping for the Onset of a Two-Band Superconducting Ground State in SrTiO3−δ

In doped SrTiO3 superconductivity persists down to an exceptionally low concentration of mobile electrons. This restricts the relevant energy window and possible pairing scenarios. We present a study of quantum oscillations and superconducting transition temperature Tc as the carrier density is tuned from 1017 to 1020 cm−3 and identify two critical doping levels corresponding to the filling thresholds of the upper bands. At the first critical doping, which separates the single-band and the two-band superconducting regimes in oxygen-deficient samples, the steady increase of Tc with carrier concentration suddenly stops.

Near this doping level, the energy dispersion in the lowest band displays a downward deviation from parabolic behavior. The results impose new constraints for microscopic pairing scenarios.

 

Left : a new frequency emerges in the Shubnikov–de Haas data in the vicinity of nc1. When the carrier density is below nc1, quantum oscillations display a single periodicity with split peaks and each peak is more prominent than its preceding neighbor (a).With increasing carrier density, a second frequency emerges on top of the first one (b)–(d). Data are plotted as a function of the inverse of magnetic field normalized by the principal frequency F1 in order to simplify comparison. The Fermi surface of the lower band according to Ref. [13] is shown in panel (e) and its projection along the three high-symmetry axes in panels (f) and (g). In multidomain crystals, the two possible Fermi cross sections give rise to split peaks in quantum oscillations.

Lire l’article Sur Physical Review Letters

 

Contact : Gabriel Seyfarth, Steffen Krämer