In Situ Preparation of Superconducting Infinite-Layer Nickelate Thin Films with Atomically Flat Surface.
basic_science · Level V
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- Also identified by DOI 10.1002/adma.202401342.
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Abstract
Since their discovery, the infinite-layer nickelates have been regarded as an appealing system for gaining deeper insights into high-temperature superconductivity (HTSC). However, the synthesis of superconducting samples has been proven to be challenging. Here, an ultrahigh vacuum (UHV) <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mtext>in situ</mtext></mrow> <annotation>${\mathrm{\text{in situ}}}$</annotation></semantics> </math> reduction method is developed using atomic hydrogen as a reducing agent and is applied in the lanthanum nickelate system. The reduction parameters, including the reduction temperature (T<sub>R</sub>) and hydrogen pressure (P<sub>H</sub>), are systematically explored. It is found that the reduction window for achieving superconducting transition is quite wide, reaching nearly 80°C in T<sub>R</sub> and three orders of magnitude in P<sub>H</sub> when the reduction time is set to 30 min. And there exists an optimal P<sub>H</sub> for achieving the highest T<sub>c</sub> if both T<sub>R</sub> and reduction time are fixed. More prominently, as confirmed by atomic force microscopy and scanning transmission electron microscopy, the atomically flat surface can be preserved during the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mtext>in situ</mtext></mrow> <annotation>${\mathrm{\text{in situ}}}$</annotation></semantics> </math> reduction process, providing advantages over the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mtext>ex situ</mtext></mrow> <annotation>${\mathrm{\text{ex situ}}}$</annotation></semantics> </math> CaH<sub>2</sub> method for surface-sensitive experiments.