Experimental Evidence for a Glass forming "Stripe Liquid" in the Magnetic Ground State of La1.65Eu0.2Sr0.15CuO4

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We report measurements of the longitudinal (¹³⁹T₁⁻¹) and transverse (¹³⁹T₂⁻¹) decay rates of the magnetization of ¹³⁹La nuclei performed in a high quality single crystal of La₁.₆₅Eu₀.₂Sr₀.₁₅CuO₄. We observe a dramatic slowing of the Cu 3d spins manifested as a sharp increase of both ¹³⁹T₁⁻¹ and ¹³⁹T₂⁻¹ below 30 K. We find that in this temperature range the fluctuations involve a unique time scale τ which diverges as (T-T A)⁻¹.⁹ with T A 5 K. This behavior is distinct from the continuous freezing observed in underdoped La₁₋ₓSrₓCuO₄ which involves a distribution of energy barriers. By contrast, in La₁.₆₅Eu₀.₂Sr₀.₁₅CuO₄, the freezing below 30K is intrinsic to its magnetic ground state and the observed power law supports the existence of a glass forming "charge stripe liquid".