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

分子晶体超导性和磁性多能带效应的理论研究

基本信息

批准号：
15550010
负责人：
NAGAO Hidemi
金额：
$ 1.22万
依托单位：
KANAZAWA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

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

许多能带在许多间隙超导中起着重要的作用，例如MgB_2超导体。从多带的重要性出发，从理论上研究了多带引起的超导隙等新的物理性质。我们这个项目的目的是：(1)研究超导的多带效应，(2)研究磁性的多带效应并讨论新磁性质的可能性，(3)研究分子晶体中的多带效应。在这个项目中，我们利用格林函数技术和一些多波段模型研究了超导性和磁性的多波段效应。在超导的多带效应中，我们得到了多带系统的超导隙比单带系统的超导隙更稳定。多带超导的转变温度高于单带超导的转变温度。带间有效的双电子对散射过程对多带超导性的研究具有重要意义。我们还研究了超导与对电子散射过程和电子-声子相互作用的有效电子相互作用的合作机制。在单带模型中，如BCS模型，有效电子相互作用应为负的。然而，在多带系统中，即使有效电子相互作用变为正或负，也会出现多带超导性。在磁性的多带效应中，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成铁磁性的，而在多带系统中，空穴掺杂则出现反铁磁性的相互作用。我们研究了有机晶体中人字晶格和两层方形晶格的磁性和超导性。在两层方形晶格中，我们获得了通过多带效应可以预期的有趣的磁性，并发现了在这种两层晶格中多带超导的可能性。少