1 Department of Physics, Technical University of Denmark2 Neutrons and X-rays for Materials Physics, Department of Physics, Technical University of Denmark3 University of Copenhagen4 École Polytechnique Fédérale de Lausanne5 Paul Scherrer Institut6 Dresden University of Technology7 Technische Universität München8 Hokkaido University9 Muroran Institute of Technology10 Swiss Federal Institute of Technology11 Paul Scherrer Institut12 Hokkaido University13 Muroran Institute of Technology14 Swiss Federal Institute of Technology
We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductorLa1.88Sr0.12CuO4 (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 La1.88Sr0.12CuO4. The difference between TN and Tf implies that the significant enhancement in a magnetic field of nominally elastic incommensurate scattering is caused by strictly inelastic 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.
Physical Review B (condensed Matter and Materials Physics), 2013, Vol 87, Issue 14