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Dimensional Crossovers in the Doped Ladder System Spin Gap, Superconductivity and Interladd.pdf

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a r X i v : c o n d - m a t / 9 8 0 2 1 8 5 v 1 [ c o n d - m a t .s u p r - c o n ] 1 8 F e b 1 9 9 8 typeset using JPSJ.sty ver.0.7f Dimensional Crossovers in the Doped Ladder System: Spin Gap, Superconductivity and Interladder Coherent Band Motion Jun-ichiro Kishine? and Kenji Yonemitsu Department of Theoretical Studies, Institute for Molecular Science, Okazaki 444-8585, Japan (Received December 5, 1997) Based on the perturbative renormalization group (PRG) approach, we have studied dimensional crossovers in Hubbard ladders coupled via weak interladder one-particle hopping, t⊥. We found that the one-particle crossover is strongly suppressed through growth of the intraladder scattering processes which lead the isolated Hubbard ladder system toward the spin gap metal (SGM) phase. Consequently when t⊥ sets in, there exists, for any finite intraladder Hubbard repulsion, U 0, the region where the two- particle crossover dominates the one-particle crossover and consequently the d-wave superconducting transition, which is regarded as a bipolaron condensation, occurs. By solving the scaling equations for the interladder one-particle and two-particle hopping amplitudes, we give phase diagrams of the system with respect to U , t⊥0 (initial value of t⊥) and the temperature, T . We compared the above dimensional crossovers with those in a weakly coupled chain system, clarifying the difference between them. KEYWORDS: doped ladder, dimensional crossover, perturbative renormalization-group, spin gap metal, bipolaron condensation, d-wave superconductivity §1. Introduction Magnetic and electronic properties of ladder materials have attracted great interest. [1] Central to these issues are the effects of the unusual spin-liquid state with a spin excitation gap in the undoped parent system on the electronic conduction in the doped system. Last year Uehara et al. [2] discovered a superconductivity signal in the doped ladder system, Sr14?xCaxCu24O41, under pressure. The comp
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