Xiao Lin, LPEM and Zhejiang University

Jeudi 13 Decembre, 16h
Amphi Howleck, Esc C, 1ème etage

Superconductivity and Fermi Surface evolution in SrTiO3

Xiao Lin
LPEM and Zhejiang University

Superconductivity and Fermi surface of bulk SrTiO3.
SrTiO3 is a large gap insulator which upon the introduction of n-type carriers under goes superconducting below 1K. Discovered in 1964, it has been the first member of a loose family of semiconducting superconductors, which now includes column IV-A elements. The non-monotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. We present a study of sub-Kelvin Nernst effect combined with other transport coefficients in samples with carrier densities, which range over three orders of magnitude. We find that down to a carrier density as low as 5.5 1017 cm-3 (corresponding to removal of one oxygen out of 105) both a superconducting ground state and a sharp Fermi surface survive. The most dilute superconductor currently known has therefore a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. Three electronic bands centered at Γ point are filled successfully by introducing electrons. Our experiment identifies two critical dopings at which the second and third bands start to be filled.

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