Yueying Li

Abstract The pairing mechanism in cuprates remains as one of the most challenging issues in condensed matter physics. Recently, superconductivity was discovered in thin films of the infinite-layer nickelate Nd 1-x Sr x NiO 2 (x = 0.12–0.25) which is believed to have the similar 3d 9 orbital electrons as that in cuprates. Here we report single-particle tunneling measurements on the superconducting nickelate thin films. We find predominantly two types of tunneling spectra, one shows a V-shape feature which can be fitted well by a d -wave gap function with gap maximum of about 3.9 meV, another one exhibits a full gap of about 2.35 meV. Some spectra demonstrate mixed contributions of these two components. Combining with theoretical calculations, we attribute the d -wave gap to the pairing potential of the $${\mathrm{Ni - }}3d_{x^2 - y^2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Ni-</mml:mi> <mml:mn>3</mml:mn> <mml:msub> <mml:mrow> <mml:mi>d</mml:mi> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo>−</mml:mo> <mml:msup> <mml:mrow> <mml:mi>y</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:msub> </mml:math> orbital. Several possible reasons are given for explaining the full gap feature. Our results indicate both similarities and distinctions between the newly found Ni-based superconductors and cuprates.

Abstract Freestanding perovskite oxide membranes have drawn great attention recently since they offer exceptional structural tunability and stacking ability, providing new opportunities in fundamental research and potential device applications in silicon‐based semiconductor technology. Among different types of sacrificial layers, the (Ca, Sr, Ba) 3 Al 2 O 6 compounds are most widely used since they can be dissolved in water and prepare high‐quality perovskite oxide membranes with clean and sharp surfaces and interfaces; However, the typical transfer process takes a long time (up to hours) in obtaining millimeter‐size freestanding membranes, let alone realize wafer‐scale samples with high yield. Here, a new member of the SrO‐Al 2 O 3 family, Sr 4 Al 2 O 7 is introduced, and its high dissolution rate, ≈10 times higher than that of Sr 3 Al 2 O 6 is demonstrated. The high‐dissolution‐rate of Sr 4 Al 2 O 7 is most likely related to the more discrete Al‐O networks and higher concentration of water‐soluble Sr‐O species in this compound. This work significantly facilitates the preparation of freestanding membranes and sheds light on the integration of multifunctional perovskite oxides in practical electronic devices.

Abstract After being expected to be a promising analog to cuprates for decades, superconductivity has recently been discovered in infinite‐layer nickelates, providing new opportunities to explore mechanisms of high‐temperature superconductivity. However, in sharp contrast to the single‐band and anisotropic superconductivity in cuprates, nickelates exhibit a multi‐band electronic structure and an unexpected isotropic superconductivity as reported recently, which challenges the cuprate‐like picture in nickelates. Here, it is shown that strong anisotropic magnetotransport behaviors exist in La‐based nickelate films with enhanced crystallinity and superconductivity ( = 18.8 K, = 16.5 K). The upper critical fields are anisotropic and violate the estimated Bardeen–Cooper–Schrieffer (BCS) Pauli limit () for in‐plane magnetic fields. Moreover, the anisotropic superconductivity is further manifested by the cusp‐like peak of the angle‐dependent T c and the vortex motion anisotropy under external magnetic fields.