Superconductivity in infinite-layer nickelate La _1−x Ca _x NiO ₂ thin films

Abstract

We report the observation of superconductivity in infinite-layer Ca-doped LaNiO 2 (La 1− x Ca x NiO 2 ) thin films and construct their phase diagram. Unlike the metal-insulator transition in Nd- and Pr-based nickelates, the undoped and underdoped La 1− x Ca x NiO 2 thin films are entirely insulating from 300 K down to 2 K. A superconducting dome is observed at 0.15 < x < 0.3 with weakly insulating behavior at the overdoped regime. Moreover, the sign of the Hall coefficient R H changes at low temperature for samples with a higher doping level. However, distinct from the Nd- and Pr-based nickelates, the R H -sign-change temperature remains at around 35 K as the doping increases, which begs further theoretical and experimental investigation to reveal the role of the 4f orbital to the (multi)band nature of the superconducting nickelates. Our results also emphasize a notable role of lattice correlation on the multiband structures of the infinite-layer nickelates.

Limits to the strain engineering of layered square-planar nickelate thin films

“…Films reduced on LaAlO 3 become insulating and form compressive strain-induced c-axis canting defects, while Nd 4 Ni 3 O 8 films on NdGaO 3 are metallic. This work provides a pathway to the synthesis of Nd n+1 Ni n O 2n+2 thin films and sets limits on the ability to strain engineer these compounds via epitaxy.The discovery of superconductivity in infinite-layer Nd 0.8 Sr 0.2 NiO 2 thin films reignited an interest in the nickelates as cuprate analogues [1][2][3][4][5][6][7][8][9][10][11] . More broadly, the infinite-layer nickelates are the n = ∞ member of a homologous series of 'layered square-planar nickelates', R n+1 Ni n O 2n+2 or (RNiO 2 ) n (RO 2 ), where R = trivalent rare-earth cation and n > 1.…”

Resonant inelastic x-ray scattering data for Ruddlesden-Popper and reduced Ruddlesden-Popper nickelates

“…1a,b ]. Indeed, this approach has been validated by the discovery of superconductivity in infinite layer n = ∞ R 1- x Sr x NiO 2 , and subsequently n = 5 Nd 6 Ni 5 O 12 , generating intense scientific interest 7 – 10 .

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Electronic structure and correlations in planar trilayer nickelate Pr 4 Ni 3 O 8

“…Recently, the spotlight has been turned to square-planar nickelate materials following the breakthrough discovery of superconductivity in thin films of the planar infinite layer nickelates, Sr/Ca-doped RNiO 2 (R = Pr, Nd, La) ( 5 – 8 ), and, more recently, the five-layer variant, Nd 6 Ni 5 O 12 ( 9 ). Proposals have been put forward that the superconducting nickelate should express exotic electronic correlations similar to those found in other unconventional superconductors, such as the doped charge-transfer cuprates ( 10 – 14 ).…”