At zero temperature the sublattice magnetization of the quantum spin-1/2 Heisenberg antiferromagnet on a body-centered cubic lattice with competing first and second neighbor exchange (J1 and J2) is investigated using the non-linear spin wave theory. The zero temperature phases of the model consist of a two sublattice Néel phase for small J2 (AF1) and a collinear phase at large J2 (AF2). We show that quartic corrections due to spin-wave interactions enhance the sublattice magnetization in both the AF1 and the AF2 phase. The magnetization corrections are prominent near the classical transition point of the model and in the J2 > J1 regime. The ground state energy with quartic interactions is also calculated. It is found that up to quartic corrections the first order phase transition (previously observed in this model) between the AF1 and the AF2 phase survives.
We show that the pitfalls encountered in earlier calculations of the RKKY range function for a noninteracting one-dimensional electron gas at zero temperature can be unraveled and successfully dealt with through a proper handling of the impurity potential. The apparently straightforward evaluation of the Ruderman-Kittel-Kasuya-Yosida ͑RKKY͒ range function, or more generally, of the linear density modulation ␦n͑x͒ induced at zero temperature in a noninteracting onedimensional electron gas by a localized static impurity modeled with a ␦ function potential has proven surprisingly troublesome. Although the original calculation gave an incorrect answer, 1 more recent investigations appear to suggest that only a certain procedure, known to lead to a physically sensible answer, should be employed.
2The original and most popular procedure is based on the standard theory of linear response. 3 If the impurity potential is assumed to be of the form U͑x͒ = ͑ប 2 u /2m͒␦͑x͒ ͑where u is a suitable wave vector͒, then one haswhere L is the system length and 0 ͑q ,0͒ is the static Lindhard response function in one dimension given by
We investigate the possible types of coupling between ferroelectricity and magnetism for the zig-zag spin chain multiferroic LiCu2O2 compound. We construct a multi-order parameter phenomenological model for the material based on a group theoretical analysis. From our calculation we conclude that a coupling involving the inter-chain magnetic structure and ferroelectricity is necessary to understand the experimental results of Park et.al.[1]. Our proposed model is able to account for the electric polarization flop in the presence of an externally applied magnetic field. Furthermore, based on our theoretical model we can make specific selection rule predictions about electromagnon excitations present in the LiCu2O2 system. We also predict that the electromagnon peaks measured in an ac-conductivity measurement are field dependent.
We perform a comprehensive analysis of the bimagnon resonant inelastic x-ray scattering (RIXS) intensity spectra of the spatially frustrated J x − J y − J 2 Heisenberg model on a square lattice in both the antiferromagnetic and the collinear antiferromagnetic phase. We study the model for strong frustration and significant spatial anisotropy to highlight the key signatures of RIXS spectrum splitting which may be experimentally discernible. Based on an interacting spin wave theory study within the ladder approximation Bethe-Salpeter scheme, we find the appearance of a robust two-peak structure over a wide range of the transferred momenta in both magnetically ordered phases. The unfrustrated model has a single-peak structure with a two-peak splitting originating due to spatial anisotropy and frustrated interactions. Our predicted two-peak structure from both magnetically ordered regime can be realized in iron pnictides. PACS number(s): 78.70. Ck, 75.10.Jm
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