Theoretical investigation of the phase diagram of high-Tc superconductors

这个联合Forschergruppe的基本新点是研究高温超导化合物的整体相图以及不同相之间的竞争，在样品制备、实验和理论模拟之间紧密协调。不同的实验技术提供了关于这些化合物的热力学和元素激发的所有基本信息。在各种互补的和部分新的理论技术的基础上，即量子蒙特卡罗(QMC)、结合量子蒙特卡罗的变分团簇技术和新的收缩重整化群概念(CORE)，我们将直接利用这一实验输入来澄清目前仍然悬而未决的问题，即什么是“普遍相关”，什么是“物质特异性”。这是在接下来的步骤中回答对理解高T_c现象至关重要的问题的必要前提，并与实验密切相关：需要研究的关键问题涉及相图的不对称性(n掺杂与p掺杂)、电荷载流子与玻色子激发的相关耦合、电子-声子相互作用在配对机制中的作用、赝隙“相”的性质，以及相当一般地，在“高能”(从EV到J序)下的微观相互作用与在很低温度下相互竞争的观察相之间的联系。

The essential new point of this joint Forschergruppe is to study the global phase diagram of the high-temperature superconducting compounds and the competition between the different phases in a tightly coordinated effort between sample preparation, experiment and theoretical modeling. The different experimental techniques yield all essential information on the thermodynamics and the elementary excitations in these compounds. On the basis of a variety of complementary and partly new theoretical techniques, namely quantum Monte-Carlo (QMC), variational cluster techniques going to the infinite-lattice limit combined with QMC, and new contractor renormalizationgroup concepts (CORE), we will directly use this experimental input to clarify the at present still unresolved issue of what is of "general relevance" and what is more "material specific". This is a necessary precondition to answer, in a subsequent step and again in close connection with experiment, questions that are central for an understanding of the high-Tc phenomenon: Crucial questions to be investigated concern the asymmetry of the phase diagram (n- vs. p -doping), the relevant couplings of charge carriers to bosonic excitations, the role of electron-phonon interaction in the pairing mechanism, the nature of the pseudo-gap "phase", and, quite generally, the connection of the microscopic interactions at "high energy" (from eV to order J ) with the observed phases competing with each other at very low temperatures.