Theoretical investigation of the phase diagram of high-Tc superconductors

该联合Forschergruppe的重要新观点是在样品制备、实验和理论建模的紧密协调下，研究高温超导化合物的整体相图和不同相之间的竞争。不同的实验技术可以得到关于这些化合物的热力学和基本激发的所有基本信息。基于各种互补的部分新的理论技术，即量子蒙特卡罗（QMC），与QMC结合的无限晶格极限的变分聚类技术，以及新的承包商重整化群概念（CORE），我们将直接使用这一实验输入来澄清目前仍未解决的问题，即什么是“一般相关性”，什么是更“材料特异性”。这是一个必要的先决条件，在接下来的步骤中，再次与实验密切相关，回答对理解高tc现象至关重要的问题：需要研究的关键问题涉及相图的不对称性（n- vs -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，伪间隙“相”的性质，以及通常情况下，“高能”（从eV到J阶）微观相互作用与观察到的相在极低温度下相互竞争的联系。

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.