Glassy low-energy spin fluctuations and anisotropy gap in La sub(1.88)Sr sub(0.12)CuO sub(4)

• Published in: Physical review. B, Condensed matter and materials physics Vol. 87; no. 14
• Main Authors: Romer, A T, Chang, J, Christensen, N B, Andersen, B M, Lefmann, K, Mahler, L, Gavilano, J, Gilardi, R, Niedermayer, Ch, Ronnow, H M
• Format: Journal Article
• Language: English
• Published: 01-04-2013
• Subjects: AMORPHOUS STRUCTURE; Anisotropy; Asymptotic properties; COPPER OXIDE; Elastic scattering; Fluctuation; GLASSES; Glassy; Low energy; MAGNETIC FIELD; Magnetic fields; Neutron scattering; PROPERTIES; SCATTERING
• ISSN: 1098-0121; 1550-235X

We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductor La sub(1.88)Sr sub(0.12)CuO sub(4) (T sub(c) = 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 T sub(N) [Asymptotically = to] T sub(c) inferred from elastic neutron scattering and the freezing temperature T sub([functionof]) [Asymptotically = to] 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 T sub([functionof]), 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 La sub(1.875)Ba sub(0.125)CuO sub(4). The difference between T sub(N) and T sub([functionof]) 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 T sub([functionof]) and T sub(c)- which is not resolved in the present experiment. Combining the results obtained from our study of La sub(1.88)Sr sub(0.12)CuO sub(4) 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 T sub([functionof]) (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.