Ni-Driven Evolution of Pseudogap and Superconducting Gap in Underdoped Cuprate

In the presented study, Ni impurity is used to probe pseudogap and superconducting gap in underdoped cuprate La1.85Sr0.15CuO4. The longitudinal magnetoresistance measurements reveal presence of local maximum at same temperature Tmax, below which zero-field resistivity parallel-resistor model deviates from its T2-dependence. Tracking systematic evolution with content y allows equating Tmax T*. rate closing by magnetic field consistent spin-paramagnetic effect, also main pair-breaking process destroying superconductivity configuration. thermal energy scale kBT* for y=0 equal relevant Zeeman scale. With increasing y, both scales separate each other. increased Stoner factor partially responsible enhancement Pauli effect decrease limiting y.