Fincher-Burke spin excitations and ω/T scaling in insulating La_1.95Sr_0.05CuO₄

Insulating La_1.95Sr_0.05CuO₄ shares with superconducting cuprates the same Fincher-Burke spin excitations, which usually are observed in itinerant antiferromagnets. The local spectral function satisfies ω/T scaling above ∼16 K for this incommensurate insulating cuprate, together with previous results in commensurate insulating and incommensurate superconducting cuprates, further supporting the general prediction for square-lattice quantum spin S = 1/2 systems. The width of incommensurate peaks in La_1.95Sr_0.05CuO₄ scales to a similar finite value as at optimal doping, strongly suggesting that they are similarly distant from a quantum critical point. They might both be limited to a finite correlation length by partial spin-glass freezing.