Superconductivity and magnetism in ladder and chain compounds physics of (Sr,Ca)14Cu041O41

M. Uehara, N. Motoyama, M. Matsuda, H. Eisaki, J. Akimitsu



The study of ladder materials has in recent years become one of the central issues in the field of condensed matter physics. Ladder materials, which contain a structural unit composed of coupled arrays of one-dimensional (1D) chains, are considered to be an interesting intermediate step between one- and two-dimensional (2D) systems [1-5]. In fact, it is now recognized that the crossover from 1D to 2D is far from straightforward and that ladder materials by themselves exhibit a variety of new physics. Historically, studies on ladder material were motivated by the discovery of hightransition- temperature (high-Tc) superconductors occurring in 2D spin-1/2 (S=1/2) Heisenberg antiferromagnets [6]. Two theoretical predictions have particularly triggered extensive research [1,2]. First, ladders made from an even number of spin-1/2 Heisenberg chains (even-leg ladders) are expected to have a unique spin-liquid ground state with short range spin correlation, where there exists a finite energy gap ("spin gap") to the lowest excited state. The spin gap, more frequently called the pseudogap, is a key feature of high-Tc superconductors, particularly in the low carrier concentration region. Ladder materials are in this context considered to be good references to gain insights into the pseudogap physics of high-Tc superconductors. Second, and a more intriguing hypothesis, is the possible occurrence of superconductivity in even-leg ladders when they are doped with holes, similar to the high-Tc materials in which holes are doped into 2D copper-oxygen (CuO2) planes. The symmetry of pairing is predicted to be d-wave like [7], adding to the similarities between doped ladders and doped 2D planes. Stimulated by these theoretical suggestions, intensive experimental studies have been carried out, with a variety of cuprate ladder materials having been newly discovered. For instance, (i) the existence of a spin gap was confirmed for SrCu 2O3, a prototype of a twoladder compound [8,9], (ii) hole-doping into two-legged ladders was first achieved on LaCuO2.5 by replacing La with Sr [10], and (iii) superconductivity at 12.5 K was observed in Sr14-xCaxCu24O41 under a pressure of 3 GPa [11]. Here, we review experimental results on cuprate spin ladder materials, emphasizing those for Sr14-xCaxCu 24O41. In Sec. 1.2, brief theoretical background is provided, while Sec. 1.3 introduces typical cuprate spin ladder materials. In Chap. 2, we review the magnetic properties of hole-doped edge-sharing S=1/2 chains, a constituent of (Sr,Ca)14Cu24O41, after which the normal state properties of (Sr,Ca)14Cu24O41 are considered in Chap. 3, with emphasis on the effect of Ca substitution on charge dynamics of hole-doped two-leg ladders. Superconducting properties are then discussed in Chap. 4, being followed by Chap. 5 which discusses the consistency between theory and experiments of ladder and summarizes novel physical insights obtained by a series of experiments on (Sr,Ca)14Cu24O 41. Readers should note that our review is in addition to other excellent reviews on spin ladder system [3-5].

ホスト出版物のタイトルFrontiers in Magnetic Materials
出版社Springer Berlin Heidelberg
ISBN(印刷版)354024512X, 9783540245124
出版ステータスPublished - 12月 1 2005

ASJC Scopus subject areas

  • 物理学および天文学(全般)


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