Ultrathin two-dimensional superconductivity with strong spin-orbit coupling.
We report on a study of epitaxially grown ultrathin Pb films that are only a few atoms thick and have parallel critical magnetic fields much higher than the expected limit set by the interaction of electron spins with a magnetic field, that is, the Clogston-Chandrasekhar limit. The epitaxial thin films are classified as dirty-limit superconductors because their mean-free paths, which are limited by surface scattering, are smaller than their superconducting coherence lengths. The uniformity of superconductivity in these thin films is established by comparing scanning tunneling spectroscopy, scanning superconducting quantum interference device (SQUID) magnetometry, double-coil mutual inductance, and magneto-transport, data that provide average superfluid rigidity on length scales covering the range from microscopic to macroscopic. We argue that the survival of superconductivity at Zeeman energies much larger than the superconducting gap can be understood only as the consequence of strong spin-orbit coupling that, together with substrate-induced inversion-symmetry breaking, produces spin splitting in the normal-state energy bands that is much larger than the superconductor's energy gap.
Department of Physics, The University of Texas at Austin, Austin, TX 78712;
Hyoungdo
H
Nam
Department of Physics, The University of Texas at Austin, Austin, TX 78712;
Hua
H
Chen
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803;
Tijiang
T
Liu
Department of Physics, The University of Texas at Austin, Austin, TX 78712;
Jisun
J
Kim
Department of Physics, The University of Texas at Austin, Austin, TX 78712;
Chendong
C
Zhang
Department of Physics, The Ohio State University, Columbus, OH 43210;
Jie
J
Yong
Department of Physics, The Ohio State University, Columbus, OH 43210;
Thomas R
TR
Lemberger
Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305.
Philip A
PA
Kratz
Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305.
John R
JR
Kirtley
Department of Physics and Applied Physics, Stanford University, Stanford, CA 94305.
Kathryn
K
Moler
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803;
Philip W
PW
Adams
Department of Physics, The University of Texas at Austin, Austin, TX 78712; macd@physics.utexas.edu shih@physics.utexas.edu.
Allan H
AH
MacDonald
Department of Physics, The University of Texas at Austin, Austin, TX 78712; macd@physics.utexas.edu shih@physics.utexas.edu.
Chih-Kang
CK
Shih
Rashba; Zeeman; spin–orbit coupling; superconductivity; ultrathin film