THEORETICAL STUDIES ON MANY-BAND EFFECTS ON SUPERCONDUCTIVITY AND MAGNETISM IN MOLECULAR CRYSTALS

在MgB_2等带隙超导体中，多个能带起着重要的作用。从多带的重要性出发，从理论上研究了多带引起的超导带隙等新的物理性质。本计画的目的是：（1）研究超导性的多带效应;（2）研究磁性的多带效应并探讨新磁性的可能性;（3）研究分子晶体中的多带效应。本项目利用绿色函数技术和一些多带模型研究了多带效应对超导性和磁性的影响，在多带效应对超导性的影响中，我们得到了带系超导带隙比单带系超导带隙更稳定的结论。多带超导转变温度比单带超导转变温度高。一种有效的双电子对散射 ...更多信息 带间过程对实现多带超导电性有着非常重要的作用。我们还研究了由电子-声子相互作用引起的电子对散射过程和有效电子相互作用的协同机制。在单带模型如BCS模型中，有效电子相互作用应该是负的。然而，在多带系统中，即使有效电子相互作用变为正或负，也会出现多带超导。我们发现，在多带系统中，有效的电子-电子相互作用在半填充时变为铁磁，而在多带系统中，空穴掺杂则出现反铁磁相互作用。有机晶体中的层状正方形晶格。在双层正方晶格中，我们得到了由多带效应引起的有趣的磁性，并发现了在这种双层晶格中多带超导的可能性。少

Many bands play an important role of many gap superconductivity such as MgB_2 superconductor. Form viewpoint of the importance of many-band, we have theoretically investigated new physical properties such as superconducting gaps etc. arising from many-band. Our purposes of this project are (1) to investigate many-band effects on superconductivity, (2) to investigate many-band effects on magnetism and to discuss the possibility of new magnetic properties, and (3) to investigate many-band effects in molecular crystals. In this project, we have investigated many-band effects on superconductivity and magnetism by using Green's function techniques and some many-band models.In many-band effects on superconductivity, we have obtained that the superconducting gap in namy-band systems becomes more stable than that of single band systems. The transition temperature for many-band superconductivity becomes higher than that of single band superconductivity. An effective two-electron pair scattering … More process between bands has a very important role to apper many-band superconductivity. We also have investigated a cooperative mechanism for superconductivity with the pair electron scattering process and the effective electron interactins from electron-phonon interaction. In a single band model such as BCS model, the effective electron interaction should be negative. However, In many-band systems, many-band superconductivity appears, even if the effective electron interaction becomes positive or negative.In many-band effects on magnetism, we have found that effective electron-electron interaction becomes ferromagnetic at half-filling in many-band systems and that antiferromagnetic interaction appears by hole-doping into the many-band systems.We have investigated magnetic and superconducting properties of herringbone and two-layer square lattices in organic crystals. In the two-layer square lattice, we have obtained that we can expect interesting magnetic properties by many-band effects and have also found the possibilities of many-band superconductivity in such two-layer lattices. Less