Re-entrant unconventional superconductivity induced by rare-earth substitution in Nd1-xEuxNiO2 thin films

Abstract

High temperature superconductivity is typically associated with strong coupling and a large superconducting gap, yet these characteristics have not been demonstrated in the nickelates. Here, we provide experimental evidence that Eu substitution in the spacer layer of Nd1-xEuxNiO2 (NENO) thin films enhances the superconducting gap, driving the system toward a strong-coupling regime. This is accompanied by a magnetic-exchange-driven magnetic-field-enhanced superconductivity. We investigate the upper critical magnetic field, Hc2, and superconducting gap of superconducting NENO thin films with x=0.2 to 0.35. Magnetoresistance measurements reveal magnetic-field-enhanced superconductivity in NENO films. We interpret this phenomenon as a result of interaction between magnetic Eu ions and superconducting states in the Ni dx2-y2 orbital. The upper critical magnetic field strongly violates the weak-coupling Pauli limit. Infrared spectroscopy confirms a large gap-to-Tc ratio $2\Delta k_B{T}_c\approx 5-6$, indicating a stronger coupling pairing mechanism in NENO relative to the Sr-doped NdNiO2. The substitution of Eu in the rare-earth layer provides a method to modify the superconducting gap in Nd-based nickelates, an essential factor in engineering high-Tc superconductivity in infinite-layer nickelates.

Under Review & Revision

References in corpus (7)

• A superconducting praseodymium nickelate with infinite layer structure
• Nickelate superconductivity without rare-earth magnetism: (La,Sr)NiO${}_2$
• Phase competition in trisected superconducting dome
• Orbital Selective Superconductivity in a Two-band Model of Infinite-Layer Nickelates
• ${}^{77}$Se NMR evidence for the Jaccarino-Peter mechanism in the field induced superconductor, $\lambda$(BETS)${}_2$FeCl${}_4$}
• A Nickelate Renaissance
• Novel dynamics and critical currents in fast superconducting vortices at high pulsed magnetic fields