Similar glassy features in the NMR response of pure and disordered La1.88Sr0.12CuO4

TL;DR

This study uses NMR to investigate glassy magnetic features in pure and disordered La1.88Sr0.12CuO4, revealing inhomogeneous spin-freezing behavior that appears unaffected by small atomic disorder, suggesting intrinsic glassiness.

Contribution

It demonstrates that glassy magnetic features in La1.88Sr0.12CuO4 are intrinsic and not solely caused by atomic disorder, based on NMR relaxation measurements.

Findings

Spin-freezing temperature is spatially inhomogeneous with an onset at 20 K.

The width of the T1^-1 distribution near Tg(onset) is unaffected by ~1% disorder.

Glassy features may not originate from quenched disorder.

Abstract

High Tc superconductivity in La2-xSrxCuO4 coexists with (striped and glassy) magnetic order. Here, we report NMR measurements of the 139La spin-lattice relaxation, which displays a stretched-exponential time dependence, in both pure and disordered x=0.12 single crystals. An analysis in terms of a distribution of relaxation rates T1^-1 indicates that i) the spin-freezing temperature is spatially inhomogeneous with an onset at Tg(onset)=20 K for the pristine samples, and ii) the width of the T1^-1 distribution in the vicinity of Tg(onset) is insensitive to an ~1% level of atomic disorder in CuO2 planes. This suggests that the stretched-exponential 139La relaxation, considered as a manifestation of the systems glassiness, may not arise from quenched disorder.