Strongly-overdoped La${}_{2-x}$Sr${}_x$CuO${}_4$: Evidence for Josephson-coupled grains of strongly-correlated superconductor

Abstract

The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, we present an experimental study of single-crystal and thin film samples of La${}_{2-x}$Sr${}_x$CuO${}_4$ (LSCO) with $x\ge 0.25$. In particular, measurements of bulk susceptibility on LSCO crystals with $x=0.25$ indicate an onset of diamagnetism at $T_{c1}=38.5$ K, with a sharp transition to a phase with full bulk shielding at $T_{c2}=18$ K, independent of field direction. Strikingly, the in-plane resistivity only goes to zero at $T_{c2}$. Inelastic neutron scattering on $x=0.25$ crystals confirms the presence of low-energy incommensurate magnetic excitations with reduced strength compared to lower doping levels. The ratio of the spin gap to $T_{c2}$ is anomalously large. Our results are consistent with a theoretical prediction for strongly overdoped cuprates by Spivak, Oreto, and Kivelson, in which superconductivity initially develops within disconnected self-organized grains characterized by a reduced hole concentration, with bulk superconductivity occurring only after superconductivity is induced by proximity effect in the surrounding medium of higher hole concentration. Beyond the superconducting-to-metal transition, local differential conductance measurements on an LSCO thin film suggest that regions with pairing correlations survive, but are too dilute to support superconducting order. Future experiments will be needed to test the degree to which these results apply to overdoped cuprates in general.

21 pages, 15 figures; added more sample characterizations, results for another sample, more discussion; accepted version

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• Puddle formation, persistent gaps, and non-mean-field breakdown of superconductivity in overdoped (Pb,Bi)2Sr2CuO6+δ
• Spontaneous time-reversal symmetry breaking by disorder in superconductors
• From non-metal to strange metal at the stripe-percolation transition in La${}_{2-x}$Sr${}_x$CuO${}_4$
• Simulating Superconducting Properties of Overdoped Cuprates: the Role of Inhomogeneity
• Emergent normal fluid in the superconducting ground state of overdoped cuprates
• Extended strange metal regime from superconducting puddles
• Inhomogeneity, Fluctuations, and Gap Filling in Overdoped Cuprates
• Signature of T${}_{\text{c}}$ above 111 K in Li-doped (Bi,Pb)-2223 superconductors: synergistic nature of hole concentration, coherence length and Josephson interlayer coupling
• Spin-stripe order tied to the pseudogap phase in La1.8-xEu0.2SrxCuO4
• Optical conductivity of overdoped cuprates from ab-initio out-of-plane impurity potentials
• La${}_{2-x}$Ba${}_x$CuO${}_4$ as a superconducting Rosetta Stone
• Taking a step back and looking at the superconducting dome from a distance
• Persistence of vortexlike phase fluctuations in underdoped to heavily overdoped Bi-2201 cuprates
• The Low-Temperature Phenomenology of Gap Inhomogeneity in the Cuprate Superconductors: High-Energy Granularity, Low-Energy Homogeneity, and Spectral Kinks
• Unified model of the Hall effect from insulator to overdoped compounds in cuprate superconductors
• The role of the pseudogap in cuprate superconductors revealed by the Hall effect
• Emergence of Fermi-liquid and BCS physics in overdoped cuprates