Critical Nature of the Ni Spin State in Doped <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>

Abstract

Superconductivity with ${T}_{c}\ensuremath{\approx}15\text{ }\text{ }\mathrm{K}$ was recently found in doped ${\mathrm{NdNiO}}_{2}$. The ${\mathrm{Ni}}^{1+}{\mathrm{O}}_{2}$ layers are expected to be Mott insulators, so hole doping should produce ${\mathrm{Ni}}^{2+}$ with $S=1$, incompatible with robust superconductivity. We show that the ${\mathrm{NiO}}_{2}$ layers fall inside a critical region where the large $pd$ hybridization favors a singlet $^{1}{A}_{1}$ hole-doped state like in ${\mathrm{CuO}}_{2}$. However, we find that the superexchange is about one order smaller than in cuprates, thus a magnon ``glue'' is very unlikely and another mechanism needs to be found.

Topics & Concepts