Measurement of an Enhanced Superconducting Phase and a Pronounced Anisotropy of the Energy Gap of a Strained FeSe Single Layer in FeSe /Nb:SrTiO3/KTaO3 Heterostructures Using Photoemission Spectroscopy
Abstract
Single-layer FeSe films with an extremely expanded in-plane lattice constant of 3.99±0.02 Å are fabricated by epitaxially growing FeSe /Nb:SrTiO3/KTaO3 heterostructures and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron pockets at the Brillouin zone corner are resolved with negligible hybridization between them, indicating that the symmetry of the low-energy electronic structure remains intact as a freestanding single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70 K for the iron-based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results place strong constraints on current theories.
- Publication:
-
Physical Review Letters
- Pub Date:
- March 2014
- DOI:
- 10.1103/PhysRevLett.112.107001
- Bibcode:
- 2014PhRvL.112j7001P
- Keywords:
-
- 74.20.Rp;
- 74.25.Jb;
- 74.70.Xa;
- 81.15.Hi;
- Pairing symmetries;
- Electronic structure;
- Molecular atomic ion and chemical beam epitaxy