Heinrich Röder | Searcharxiv

arXiv1997

Theory of colossal magnetoresistance

The history and recent developments in studying (colossal) magnetoresistance in perovskite manganese oxides is reviewed. We emphasize the growing evidence for strongly coupled spin, charge and lattice degrees of freedom. Together with disorder, these provide the microscopic driving forces for local and inhomogeneous textures. The modeling and experimental probes for localized charge-spin-lattice (polaron) structures, and their multiscale ordering, is discussed in terms of a growing synergy of solid state physics and materials science perspectives.

cond-mat↗

arXiv1995

Spin correlation functions in random-exchange s=1/2 XXZ chains

The decay of (disorder-averaged) static spin correlation functions at T=0 for the one-dimensional spin-1/2 XXZ antiferromagnet with uniform longitudinal coupling $JΔ$ and random transverse coupling $Jλ_i$ is investigated by numerical calculations for ensembles of finite chains. At $Δ=0$ (XX model) the calculation is based on the Jordan-Wigner mapping to free lattice fermions for chains with up to N=100 sites. At $Δ\neq 0$ Lanczos diagonalizations are carried out for chains with up to N=22 sites. The longitudinal correlation function $ $ is found to exhibit a power-law decay with an exponent that varies with $Δ$ and, for nonzero $Δ$, also with the width of the $λ_i$-distribution. The results for the transverse correlation function $ $ show a crossover from power-law decay to exponential decay as the exchange disorder is turned on.

cond-mat↗