Why Superconductivity Disappears in Very Overdoped La_2-xSr_xCuO₄

We have studied single crystals of La_2-xSr_xCuO₄ with x = 0.25 and 0.29 [1]. Magnetization shows an onset of weak diamagnetism near 38 K, independent of field direction, and a transition to bulk shielding at 18 K (4 K), respectively, where the in-plane resistivity drops to zero. Inelastic neutron scattering measurements on the x = 0.25 sample reveal incommensurate magnetic excitations, similar to results at lower doping [2] but with reduced intensity, that develop a spin gap which, relative to a superconducting transition temperature of 18 K, is anomalously large. Sample characterizations demonstrate no evidence of phase separation. Instead, we argue that the random distribution of Sr dopants allows small regions of underdoped character to develop superconducting order at an elevated temperature, with bulk superconductivity occurring at a much lower temperature, limited by Josephson coupling between these self-organized grains, as proposed in [3]. The implication is that the locally-overdoped regions are not intrinsically superconducting.



[1] Y. Li et al., arXiv:2205.01702.

[2] Y. Li et al., Phys. Rev. B 98, 224508 (2018).

[3] B. Spivak, P. Oreto, S. A. Kivelson, Phys. Rev. B 77, 214523 (2008).