Effect of Parallel Magnetic Field on Superconductivity of Ultrathin Metal Films Grown on a Cleaved GaAs Surface

Abstract

The parallel-magnetic-field H dependence of the superconducting transition temperature T c is studied for ultrathin films of In, Bi, and Al grown on GaAs(110). In the case of In films in the monolayer regime, T c exhibits a quadratic-like H dependence, which is one order of magnitude stronger than that previously observed in monolayer Pb films by the present authors [Phys. Rev. Lett. 111, 057005 (2013)]. The results are well reproduced by a model developed for an inhomogeneous two-dimensional superconducting state in the presence of a moderate Rashba spin-orbit interaction. The Rashba spin splitting is estimated to be 0.04 eV, which is much smaller than that expected for monolayer Pb films. In a few-monolayer Bi film, the suppression of T c with increasing H is comparable to that in monolayer Pb films. On the other hand, much stronger suppression, which is attributed to the Pauli paramagnetic effect, was observed for the Al film.

Surface atomic-layer superconductors with Rashba/Zeeman-type spin-orbit coupling

“…As described in Section 3.5, quench-condensed Pb monolayer films on in situ cleaved GaAs (111) substrates were found to be become superconducting around 2-3 K [96,97]. It was also revealed that the superconductivity is extremely robust against in-plane magnetic fields; the reduction in T c was found to be only 5-6% even for strong in-plane fields H ∥ exceeding several times the Pauli limit.…”

“…This sample fabrication technique, capable of fine tuning of the film coverage, has widely been used for studies on the superconductor-insulator transition in 2D systems [93][94][95]. Recently, quenchcondensed Pb and In layers on in situ cleaved GaAs (110) substrates were found to exhibit superconductivity around 2-3 K at a nominal coverage of 1 ML [96,97]. The persistent superconductivity in this coverage regime, when compared to preceding experiments, may be attributable to the usage of in situ cleaved GaAs (110) as a substrate and to an improved film crystallinity.…”

Magnetic-Field-Induced Superconductivity in Ultrathin Pb Films with Magnetic Impurities

“…The suppression of PE was explained in terms of the spin precession due to the Rashba field [5,6], which allows nonmagnetic scattering by defects to mix the spinup state and spin-down state [7]. In this study, we employ ultrathin Pb films as the host superconductor to minimize OE and PE, which act directly on conduction electrons, and investigate the magnetic-field effect on superconductivity related to magnetic impurities.…”

“…Recently, it has been demonstrated that the reduction of the superconducting transition temperature T c due to the parallel magnetic field H is extremely small (∼ 1% for 10 T) in ultrathin Pb films grown on a cleaved GaAs(110) surface [4]. The suppression of PE was explained in terms of the spin precession due to the Rashba field [5,6], which allows nonmagnetic scattering by defects to mix the spinup state and spin-down state [7]. In this study, we employ ultrathin Pb films as the host superconductor to minimize OE and PE, which act directly on conduction electrons, and investigate the magnetic-field effect on superconductivity related to magnetic impurities.…”

“…It has been predicted that a magnetic field can induce a superconducting quantum phase transition when ν s is in an appropriate range and PE is strongly reduced due to spin-orbit scattering. In ultrathin Pb films, high spinorbit scattering rate is expected to be effectively achieved by the combination of the Rashba field and nonmagnetic scattering [7]. In Fig.…”