2010/10/06 by Mukul S. Laad, Laad, Mukul S., Luis Craco +1
Physics and Astronomy · #FOS: Physical sciences #Superconductivity (cond-mat.supr-con) #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.1010.1098
9 pages, 5 figures
arxiv created 2010/10/06 · arxiv updated 2010/10/07
We consider the effects of the non-local Ising-like "core spin" correlations on the order-parameter fluctuation contribution to the resistivity and thermodynamics of metals showing Ising-like order at finite temperature. We employ the well-known cluster-variation method, and present explicit results in the pair approximation for short-range order. Our calculation generalizes earlier works, where such effects were considered in the mean-field (Ornstein-Zernicke) approximation. The mean-field (MF) transition temperature TcMF, is corrected to O(1/d), and the effect of the Ising spin fluctuations on the dc resistivity and magnetothermal responses is analyzed in detail. The method can be applied straightforwardly to lattices in arbitrary d, and, as an appealing feature, it reproduces the exact correlation length and Tc1d=0 for the 1d Ising model. We apply our results for two interesting physical cases: (i) the double-exchange model with JH>>t, where the core-spins can be approximated quite well by Ising spins, and (ii) a model of band electrons coupled to a \it localized subsystem which undergoes a nematic ordering transition coupled to an appropriate structural transition.