Two-Dimensional Superconducting State of Monolayer Pb Films Grown on GaAs(110) in a Strong Parallel Magnetic Field

Two-dimensional (2D) superconductivity was studied by magnetotransport measurements on single-atomic-layer Pb films on a cleaved GaAs(110) surface. The superconducting transition temperature shows only a weak dependence on the parallel magnetic field up to 14 T, which is higher than the Pauli paramagnetic limit. Furthermore, the perpendicular-magnetic-field dependence of the sheet resistance is almost independent of the presence of the parallel field component. These results are explained in terms of an inhomogeneous superconducting state predicted for 2D metals with a large Rashba spin splitting.

Figure 1

Zero-field superconducting transition temperature and normal-state sheet resistance as a function of the nominal thicknesses of Pb and Bi films. Different filled (red) symbols correspond to different experiments in this work. Open (blue) circles are data from Ref. 1.

Figure 2

$T$ dependence of the sheet resistance of Pb films for different atomic areal densities. Dashed (blue) curves are obtained at zero magnetic field. Solid (red) curves are obtained in parallel magnetic field of 8.5 T (for $n=7.2{\mathrm{nm}}^{-2}$) or 13.7 T (for $n=9.4$ and $11.3{\mathrm{nm}}^{-2}$). The magnetic-field angle was adjusted to $H_{\perp }=0$ using the $R_{sq}$ minimum.

Figure 3

$H_{\perp }$ dependence of the sheet resistance of the Pb film at $n=7.2{\mathrm{nm}}^{-2}$ and $T=0.51\mathrm{K}$. The solid (blue) curve is obtained for the perpendicular-magnetic-field direction ($H_{\parallel }=0$). Filled (red) circles are obtained by changing the magnetic-field angle (upper axis) at a fixed strength of 9 T.

Figure 4

$H_{\parallel }$ dependence of $\Delta T_c\equiv T_c-T_{c0}$ for Pb films with $n=9.4$ and $11.3{\mathrm{nm}}^{-2}$. The dashed lines are the best parabolic fits.