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Critical dopings and superconducting domes in doped SrTiO3

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In doped SrTiO3, superconductivity persists down to an exceptionally low concentration of mobile electrons. In this concentration range, the Fermi energy becomes more than one order of magnitude lower than the Debye energy.This severely restricts the relevant energy window for pairing and eliminates the conventional picture of superconductivity, in which electrons at Fermi level exchange virtual phonons of typical Debye energy. As the sytem is doped, theory expects multiple bands to be successively filled in the normal state. On the other hand, experiment has detected distinct superconducting gaps near optimal doping. We present a study of quantum oscillations and superconducting transition temperature, which clarifies the link between these two features. As the carrier density is tuned over three orders of magnitude, two critical doping levels are identified by our experiment. They correspond to the filling thresholds of the two upper bands.Tc presents a pronounced hump in the vicinity of the first critical doping, separating a single-band and a two-band superconductor. The one-band superconductor below this critical doping emerges as a strong-coupling extremely dilute superconductor.

This talk is part of the Quantum Matter Seminar series.

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