Department of Theoretical Physics, Ural Federal University, 620083 Ekaterinburg, Russia.
J Phys Condens Matter. 2013 Feb 27;25(8):085601. doi: 10.1088/0953-8984/25/8/085601. Epub 2013 Jan 30.
Disproportionation in 3d compounds can give rise to an unconventional electron-hole Bose liquid with a very rich phase diagram, from a Bose metal, to a charge ordering insulator and an inhomogeneous Bose-superfluid. Optimal conditions for disproportionation driven high-T(c) superconductivity are shown to be realized only for several Jahn-Teller d(n) configurations that permit the formation of well defined local composite bosons. These are the high-spin d(4), low-spin d(7), and d(9) configurations given the octahedral crystal field, and the d(1), high-spin d(6) configurations given the tetrahedral crystal field. The disproportionation reaction has a peculiar 'anti-Jahn-Teller' character lifting the bare orbital degeneracy. Superconductivity in the d(4) and d(6) systems at variance with d(1), d(7), and d(9) systems implies unavoidable coexistence of the spin-triplet composite bosons and the magnetic lattice. We argue that unconventional high-T(c) superconductivity, observed in quasi-2d cuprates with tetragonally distorted CuO(6) octahedra and iron-based layered pnictides/chalcogenides with tetrahedrally coordinated Fe(2+) ions presents a key argument to support the fact that the disproportionation scenario is at work in these compounds.
3d 化合物中的歧化作用可能导致非常规的电子-空穴玻色液体，具有非常丰富的相图，从玻色金属到电荷有序绝缘体和非均匀玻色超流体。歧化驱动高温超导的最佳条件被证明只在几种 Jahn-Teller d(n) 构型下实现，这些构型允许形成定义明确的局部复合玻色子。对于八面体晶体场，这些是高自旋 d(4)、低自旋 d(7)和 d(9)构型，而对于四面体晶体场，则是 d(1)、高自旋 d(6)构型。歧化反应具有特殊的“反 Jahn-Teller”性质，消除了裸轨道简并。与 d(1)、d(7)和 d(9)系统不同，d(4)和 d(6)系统中的超导意味着自旋三重态复合玻色子和磁晶格不可避免地共存。我们认为，在具有四方畸变的 CuO(6)八面体的准 2d 铜酸盐和具有四面体配位 Fe(2+)离子的铁基层状磷化物/硫属化物中观察到的非常规高温超导提供了一个关键论据，支持在这些化合物中歧化方案正在起作用的事实。
