Superconductivity with enhanced critical current density in ultrathin infinite-layer nickelate films

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The thickness-dependent properties remain largely unknown in infinite-layer nickelate (RNiO2) superconductors due to challenges in materials synthesis. Herein, by devising atomically precise heterostructures of La0.8Sr0.2NiO2/LaNiO2 (LSNO/LNO), we are able to stabilize robust superconductivity with nearly undegraded superconducting transition temperature in a six-unit-cell (UC)-thick LSNO layer. The superconducting transition can be restored for a 4-UC LSNO layer when an LNO buffer is employed to isolate LSNO from the SrTiO3 (STO) substrate, underscoring the crucial role of the bottom interface in suppressing the superconductivity of ultrathin LSNO. This is further supported by scanning transmission electron microscopy, which reveals the formation of an interfacial layer of 2 ~ 3 UC thick with large c/a ratio at STO/LSNO interface. The upper critical field exhibits strong anisotropy and is virtually independent of LSNO thickness. Strikingly, the critical current density increases exponentially upon reducing LSNO thickness below 15 UC, reaching a maximum value of 780 KA/cm2 at 2 K for 8-UC LSNO, which is two to three times larger than LSNO thick films and previously reported RNiO2 films. Our results not only shed important insights into the interface effects in RNiO2 superconductors, but also suggest a viable approach to the exploration of possible interface superconductivity in RNiO2 heterostructures. Thickness-dependent properties remain largely unknown in infinite-layer nickelate superconductors due to challenges in materials synthesis. Here, atomically precise heterostructures of LSNO/LNO are synthesized, showing robust superconductivity with a nearly undegraded superconducting transition temperature in a six-unit-cell-thick LSNO layer.

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