Magnetic order inLa1.9Sr0.1CuO4

Abstract

We report two-magnon Raman scattering from La1.9Sr0.1CuO4, which has a suppressed Tc=12 K, as the temperature is lowered below 37 K and an ordered spin phase is formed. The two-magnon Raman intensity increases with decreasing temperature. The magnetic scattering in La1.9Sr0.1CuO4 is totally different from that reported in the parent compound La2CuO4. We analyze the line shape of the two-magnon scattering within the traditional Loudon-Fleury theory and find the superexchange constant J=1052 cm −1 . The calculation of the frequency moment suggests that the quantum fluctuations are very weak in the system. The room temperature Raman scattering from La2CuO4 is also measured. Strong features appear in the one-phonon spectrum at the frequencies of the longitudinal optical (LO) infrared modes which we suggest become Raman active through a Fröhlich-interaction.

Monte Carlo study of the superfluid weight in doped antiferromagnets

“…Specifically, the elastic neutron-scattering measurements 13 in pristine La 2−x Sr x CuO 4 , with x = 0.10, 0.12, have established the presence of static long-range antiferromagnetic order in the superconducting ground state, suggested by earlier work. 14 This conclusion is supported also by the subsequent observation of conventional two-magnon Raman scattering 15 in the same material.…”

“…Using the experimental data of Panagopoulos et al 12 for λ ab (T ) on the underdoped La 2−x Sr x CuO 4 , with x = 0.10, and the structural parameter 29 d = 6.64 Å, we depict in Fig. 2 by triangles the corresponding experimental values (15) for the superfluid weight vs temperature. As a result of the weak coupling between the copper-oxide layers, the experimental data display no KT discontinuity but rather a continuous drop of the superfluid weight to zero, at a specific temperature value, that is not simply related to the ideal KT transition temperature of a copper-oxide monolayer.…”