Negligible oxygen vacancies, low critical current density, electric-field modulation, in-plane anisotropic and high-field transport of a superconducting Nd_0.8Sr_0.2NiO₂/SrTiO₃ heterostructure

The emerging Ni-based superconducting oxide thin films are rather intriguing to the entire condensed matter physics. Here, we report some brief experimental results on transport measurements for a 14-nm-thick superconducting Nd_0.8Sr_0.2NiO₂/SrTiO₃ thin-film heterostructure with an onset transition temperature of ~ 9.5 K. Photoluminescence measurements reveal that there is negligible oxygen vacancy creation in the SrTiO₃ substrate during thin-film deposition and post chemical reduction for the Nd_0.8Sr_0.2NiO₂/SrTiO₃ heterostructure. It was found that the critical current density of the Nd_0.8Sr_0.2NiO₂/SrTiO₃ thin-film heterostructure is relatively small, ~ 4 × 10³ A·cm⁻². Although the surface steps of SrTiO₃ substrates lead to an anisotropy for in-plane resistivity, the superconducting transition temperatures are almost the same. The out-of-plane magnetotransport measurements yield an upper critical field of ~ 11.4 T and an estimated in-plane Ginzburg–Landau coherence length of ~ 5.4 nm. High-field magnetotransport measurements up to 50 T reveal anisotropic critical fields at 1.8 K for three different measurement geometries and a complicated Hall effect. An electric field applied via the SrTiO₃ substrate slightly varies the superconducting transition temperature. These experimental results could be useful for this rapidly developing field.

新兴镍基超导氧化物薄膜在整个凝聚态物理领域引起了很大关注。在此论文中, 我们通过电输运测量研究了一个 14 nm 厚的超导 Nd_0.8Sr_0.2NiO₂/SrTiO₃ 异质结样品。这个样品的起始超导转变温度约为 9.5 K。光致荧光谱测量发现: 此异质结中 SrTiO₃基片内部的氧空位含量极少。这说明纳米薄膜的沉积及后续化学氢化过程并没有在 SrTiO₃ 单晶基片中引入显著的氧空位。我们还发现这种超导异质结的临界电流密度相对很低, 约为 4 × 10³ A·cm⁻²。虽然 SrTiO₃ 单晶基片的表面台阶诱发了面内电阻率的各向异性, 但超导转变温度却几乎不受影响。在薄膜表面的垂直方向施加磁场的电输运测量揭示出此超导样品的上临界场约为11.4 T, 对应面内Ginzburg-Landau相干长度约为 5.4 nm。高达 50 T 的强磁场电输运测量研究发现: 1.8 K 下, 完全破坏超导态使得样品达到正常态电阻率的临界磁场具有各向异性。