Coexistence of Antiferromagnetic Spin Fluctuations and Superconductivity in La2SmNi2O7 Thin Films

TL;DR

This study provides experimental evidence of the coexistence and interplay of antiferromagnetic spin fluctuations and superconductivity in La2SmNi2O7 thin films, shedding light on their pairing mechanism in nickelate superconductors.

Contribution

It is the first to experimentally verify the coexistence of AFM fluctuations and superconductivity in nickelates, revealing a direct correlation crucial for understanding their pairing mechanism.

Findings

Observation of 'Mexican hat'-shaped magnetoresistance indicating coexistence

Identification of a crossover field B* related to AFM fluctuations

Decrease of B* with temperature, vanishing near superconducting transition

Abstract

The interplay between magnetic fluctuations and superconductivity is fundamental for understanding unconventional high-temperature superconductors. In the recently discovered Ruddlesden-Popper phase nickelates-which achieve superconducting transition temperatures up to ~100 K-this connection has been theoretically predicted but experimentally unverified. Using compressively strained La2SmNi2O7 thin films, we report direct evidence for this interplay. We observe a characteristic 'Mexican hat'-shaped magnetoresistance, a signature of superconductivity coexisting with emergent antiferromagnetic (AFM) fluctuations. This distinctive feature arises from a competition between the magnetic field's suppression of AFM fluctuation-driven scattering and its suppression of superconducting fluctuations. We quantify these AFM fluctuations by a crossover field, B*, whose magnitude decreases with increasing temperature and vanishes near the superconducting onset-behavior contrasting sharply with that in high-Tc cuprates. Our results establish not merely coexistence, but also a direct and novel correlation between AFM instability and superconductivity in nickelates, offering crucial insight into their pairing mechanism.