Direct evidence of superconductivity and determination of the superfluid density in buried ultrathin FeSe grown on SrTiO3

Article

关键词: HIGH-TEMPERATURE SUPERCONDUCTIVITY;    MAGNETIC PENETRATION DEPTH;    MU-SR;    PHASE-DIAGRAM;    65 K;    FILMS;    SURFACE;    MUONS;    PSI;   

DOI  :  10.1103/PhysRevB.97.174509

来源: SCIE

【 摘 要 】

Bulk FeSe is superconducting with a critical temperature Tc congruent to 8 K and SrTiO3 is insulating in nature, yet high-temperature superconductivity has been reported at the interface between a single-layer FeSe and SrTiO3. Angle resolved photoemission spectroscopy and scanning tunneling microscopy measurements observe a gap opening at the Fermi surface below approximate to 60 K. Elucidating the microscopic properties and understanding the pairing mechanism of single-layer FeSe is of utmost importance as it is a basic building block of iron-based superconductors. Here, we use the low-energy muon spin rotation/relaxation technique to detect and quantify the supercarrier density and determine the gap symmetry in FeSe grown on SrTiO3 (100). Measurements in applied field show a temperature-dependent broadening of the field distribution below similar to 60 K, reflecting the superconducting transition and formation of a vortex state. Zero-field measurements rule out the presence of magnetism of static or fluctuating origin. From the inhomogeneous field distribution, we determine an effective sheet supercarrier density n(s)(2D) similar or equal to 6 x 10(14) cm(-2) at T -> 0 K, which is a factor of 4 larger than expected from ARPES measurements of the excess electron count per Fe of 1 monolayer FeSe. The temperature dependence of the superfluid density n(s) (T) can be well described down to similar to 10 K by simple s-wave BCS, indicating a rather clean superconducting phase with a gap of 10.2(1.1) meV. The result is a clear indication of the gradual formation of a two-dimensional vortex lattice existing over the entire large FeSe/STO interface and provides unambiguous evidence for robust superconductivity below 60 K in ultrathin FeSe.

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