Tunable two-dimensional superconductivity and spin-orbit coupling at the EuO/KTaO3(110) interface

Abstract

Unconventional quantum states, most notably the two-dimensional (2D) superconductivity, have been realized at the interfaces of oxide heterostructures where they can be effectively tuned by the gate voltage ($V_G$). Here we report that the interface between high-quality EuO (111) thin film and KTaO3 (KTO) (110) substrate shows superconductivity with onset transition temperature $T_c^{onset}$ = 1.35 K. The 2D nature of superconductivity is verified by the large anisotropy of the upper critical field and the characteristics of a Berezinskii-Kosterlitz-Thouless transition. By applying $V_G$, $T_c^{onset}$ can be tuned from ~ 1 to 1.7 K; such an enhancement can be possibly associated with a boosted spin-orbit energy ${\epsilon}_{so}$ = $\hbar$ / ${\tau}_{so}$, where ${\tau}_{so}$ is the spin-orbit relaxation time. Further analysis of ${\tau}_{so}$ based on the upper critical field ($H_{c2}$) and magnetoconductance reveals complex nature of spin-orbit coupling (SOC) at the EuO/KTO(110) interface with different mechanisms dominate the influence of SOC effects for the superconductivity and the magnetotransport in the normal state. Our results demonstrate that the SOC should be considered as an important factor determining the 2D superconductivity at oxide interfaces.