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Neutron Scattering study of Sr_2Cu_3O_4Cl_2

Y. J. Kim·R. J. Birgeneau·F. C. Chou·M. Greven·M. A. Kastner·Y. S. Lee·B. O. Wells·A. Aharony·O. Entin-Wohlman·I. Ya. Korenblit·A. B. Harris·R. W. Erwin·G. Shirane
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Abstract

We report a neutron scattering study on the tetragonal compound Sr_2Cu_3O_4Cl_2, which has two-dimensional (2D) interpenetrating Cu_I and Cu_{II} subsystems, each forming a S=1/2 square lattice quantum Heisenberg antiferromagnet (SLQHA). The mean-field ground state is degenerate, since the inter-subsystem interactions are geometrically frustrated. Magnetic neutron scattering experiments show that quantum fluctuations lift the degeneracy and cause a 2D Ising ordering of the Cu_{II} subsystem. Due to quantum fluctuations a dramatic increase of the Cu_I out-of-plane spin-wave gap is also observed. The temperature dependence and the dispersion of the spin-wave energy are quantitatively explained by spin-wave calculations which include quantum fluctuations explicitly. The values for the nearest-neighbor superexchange interactions between the Cu_I and Cu_{II} ions and between the Cu_{II} ions are determined experimentally to be J_{I-II} = -10(2)meV and J_{II}= 10.5(5)meV, respectively. Due to its small exchange interaction, J_{II}, the 2D dispersion of the Cu_{II} SLQHA can be measured over the whole Brillouin zone with thermal neutrons, and a novel dispersion at the zone boundary, predicted by theory, is confirmed. The instantaneous magnetic correlation length of the Cu_{II} SLQHA is obtained up to a very high temperature, T/J_{II}\approx 0.75. This result is compared with several theoretical predictions as well as recent experiments on the S=1/2 SLQHA.

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Y. J. Kim, R. J. Birgeneau, F. C. Chou, M. Greven, M. A. Kastner, Y. S. Lee, B. O. Wells, A. Aharony, O. Entin-Wohlman, I. Ya. Korenblit, A. B. Harris, R. W. Erwin, G. Shirane. 2000-09-21. Neutron Scattering study of Sr_2Cu_3O_4Cl_2. https://doi.org/10.1103/physrevb.64.024435

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