Superconductivity in the Parent Infinite-Layer Nickelate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>NdNiO</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math>
C. T. Parzyck, Yi Wu, Lopa Bhatt, Mingu Kang, Zachary Arthur, Tor Pedersen, Ronny Sutarto, Shiyu Fan, Jonathan Pelliciari, Valentina Bisogni, G. Herranz, Alexandru B. Georgescu, D. G. Hawthorn, Lena F. Kourkoutis, David A. Muller, Darrell G. Schlom, Kyle Shen
Abstract
We report evidence for superconductivity with onset temperatures up to 11 K in thin films of the infinite-layer nickelate parent compound <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msub> <a:mrow> <a:mi>NdNiO</a:mi> </a:mrow> <a:mrow> <a:mn>2</a:mn> </a:mrow> </a:msub> </a:mrow> </a:math> . A combination of oxide molecular beam epitaxy and atomic hydrogen reduction yields samples with high crystallinity and low residual resistivities, a substantial fraction of which exhibit superconducting transitions. We survey a large series of samples with a variety of techniques, including electrical transport, scanning transmission electron microscopy, x-ray absorption spectroscopy, and resonant inelastic x-ray scattering, to investigate the possible origins of superconductivity. We propose that superconductivity could be intrinsic to the undoped infinite-layer nickelates but suppressed by disorder due to a possibly sign-changing order parameter, a finding which would necessitate a reconsideration of the nickelate phase diagram. Another possible hypothesis is that the parent materials can be hole doped from randomly dispersed apical oxygen atoms, which would suggest an alternative pathway for achieving superconductivity.