Single-band fluorides akin to infinite-layer cuprate superconductors

Abstract Recent experimental discoveries of infinite- and finite-layer nickelate superconductors have highlighted the importance of a single-band $${d}_{{x}^{2}-{y}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <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> Fermi surface for enabling unconventional superconductivity similar to cuprates. Motivated by this, we use density functional theory (DFT) and dynamical mean-field theory (DMFT) to identify two infinite-layer fluorides—KNiF 2 and KPdF 2 —as promising candidates. Both materials exhibit strong correlations, structural stability, a single-band $${d}_{{x}^{2}-{y}^{2}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <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> Fermi surface, and an antiferromagnetic Mott insulating state for the undoped parent compound. However, in KNiF 2 , overly strong correlations suppress spin fluctuations, preventing the electron pairing and superconducting states at finite temperatures. In contrast, KPdF 2 offers tunable superconducting behavior. Using dynamical vertex approximation (DΓA), we show that 20% hole doping on SrTiO 3 and 10% electron doping on MgO substrate yield superconducting transition temperatures of 65 K and 63 K, respectively, demonstrating the material’s potential through doping and substrate engineering.