Glassy low-energy spin fluctuations and anisotropy gap in La1.88Sr0.12CuO4

TL;DR

This study investigates low-energy spin fluctuations and anisotropy gaps in La1.88Sr0.12CuO4 using neutron scattering, revealing glassy magnetic features and composition-dependent magnetic excitation characteristics near the 1/8 doping level.

Contribution

It provides detailed insights into the magnetic excitation spectrum and glassy behavior in La1.88Sr0.12CuO4, highlighting the role of composition and magnetic field effects on spin fluctuations.

Findings

Glassy features in low-energy magnetic fluctuations.

Presence of a spin anisotropy gap similar to stripe-ordered states.

Magnetic field does not significantly alter the excitation spectrum.

Abstract

We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The temperature dependence of the low-energy incommensurate magnetic fluctuations reveals distinctly glassy features. The glassiness is confirmed by the difference between the ordering temperature TN ~ Tc inferred from elastic neutron scattering and the freezing temperature Tf ~ 11 K obtained from muon spin rotation studies. The magnetic field independence of the observed excitation spectrum as well as the observation of a partial suppression of magnetic spectral weight below 0.75 meV for temperatures smaller than Tf, indicate that the stripe frozen state is capable of supporting a spin anisotropy gap, of a magnitude similar to that observed in the spin and charge stripe ordered ground state of La1.875Ba0.125CuO4. The difference between TN and Tf implies that the significant enhancement in a magnetic field of nominally elastic incommensurate scattering is caused by strictly in-elastic scattering -- at least in the temperature range between Tf and Tc -- which is not resolved in the present experiment. Combining the results obtained from our study of La1.88Sr0.12CuO4 with a critical reappraisal of published neutron scattering work on samples with chemical composition close to p=0.12, where local probes indicate a sharp maximum in Tf(p), we arrive at the view that the low-energy fluctuations are strongly dependent on composition in this regime, with anisotropy gaps dominating only sufficiently close to p=0.12 and superconducting spin gaps dominating elsewhere.