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 $$T_{{{\mathrm{c}}}}^{{{{\mathrm{onset}}}}}$$ = 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, $$T_{{{\mathrm{c}}}}^{{{{\mathrm{onset}}}}}$$ can be tuned from ~1 to 1.7 K; such an enhancement can be possibly associated with a boosted spin-orbit energy $$\varepsilon _{{{{\mathrm{so}}}}} = \hbar /\tau _{{{{\mathrm{so}}}}}$$, where τ_so is the spin-orbit relaxation time. Further analysis of τ_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 dominating the influence of SOC effects on the superconductivity and the magnetotransport in the normal state. Our results demonstrate that the SOC should be considered an important factor in determining the 2D superconductivity at oxide interfaces.