铁基高温超导体的比热和极低温热输运性质研究

【作者】 丁力；

【导师】 李世燕；

【作者基本信息】 复旦大学 ， 凝聚态物理， 2010， 博士

【摘要】 自从上个世纪初超导现象首次发现以来,科学家们一直都在努力寻找拥有更高临界温度Tc的超导材料,并以寻找到室温超导体为这一领域的最大梦想之一。在经历了铜氧化物的第一次高温超导研究飞跃性进展之后,高温超导的研究热情在进入21世纪后,又慢慢陷入低潮。目前,研究人员对高温超导机理一直未达成一致看法,所以人们期望能在铜氧化物超导体以外再发现新的高温超导体系。就在2008年年初,日本科学家发现的临界温度达到26 K的LaO1-xFxFeAs高温超导体后,一系列的新型铁基高温超导体被陆续发现,从此开启了超导界新一轮的高温超导研究的热潮。在本论文中,我们将对不同体系的铁基高温超导材料的比热和极低温热输运性质等方面的实验结果进行详细的研究和讨论。本文的前三章将详细介绍研究动机和相关的理论背景,包括铁基高温超导材料的研究进展、输运性质测量的理论知识以及相关实验设备的介绍。之后的四个章节,将分别详细介绍我们对“1111”体系的SmO1-xFxFeAs以及“122”体系的Ba1-xKxFe2As2和Ca1-xNaXFe2As2的比热性质研究,另外作为研究超导体能隙结构的最有利的实验研究手段之一,将依次介绍“122”体系电子型掺杂的BaFe1.9Ni0.1As2和“11”体系FeSex的极低温热输运性质研究。本文的章节内容概要如下：第一章介绍超导以及高温超导材料的研究历程与进展,并按时间顺序详细介绍新型铁基高温超导体各种体系的发现和近期的实验和理论研究成果。第二章介绍固体的比热和热导率的基本理论及其在超导体上的研究应用,以及超导能隙在极低温热导率上的行为。第三章简要介绍本文研究所使用的实验手段,包括PPMS系统及其比热测量组件,和极低温热输运性质测量系统的实验装置,包括其工作原理和技术细节。第四章详细介绍对“1111”体系的SmO1-xFxFeAs超导体的比热性质研究。第五章详细介绍对“122”体系的Ba1-xKxFe2As2和Ca1-xNaxFe2As2的比热性质研究。第六章详细介绍对电子型掺杂的“122”体系中BaFe1.9Ni0.1As2的极低温热输运性质研究。第七章详细介绍对“11”体系的FeSex的极低温热输运性质研究。第八章对全文进行总结。更多还原

【Abstract】 Since the discovery of superconductivity at the beginning of last century, scientists have been searching for superconducting materials with higher critical temperature (Tc),and to find room temperature superconductor is one of the biggest dreams to the scientists. After the breakthrough of cuprates, the research on high Tc superconductivity is getting slow in the 21st century. At present, the physical mechanism of high Tc superconductivity is still a controversial issue, thus researchers are hoping to find new high Tc superconductors other than cuprates.Just in the early of 2008, a Japanese group announced the discovery of a new high Tc superconductor-LaO1-xFxFeAs with Tc=26 K. Since then, new series of so-called iron-based superconductors are found successively, and a new round of research on high Tc superconductor has begun.In this dissertation, we will make a particular research and discussion on the specific heat and ultra-low temperature thermal transport experimental results about several kinds of iron-based superconductor systems.In the first three chapters, we will give a detailed introduction on the research motivation and relevant theory backgrounds, including research progress on iron-based high Tc superconductors, theories on transport measurements and corresponding experimental facilities. The rest part of this dissertation will report our specific heat and ultra-low temperature thermal transport on three different kinds of iron-based high Tc superconductor materials:1111,122 and 11 systems.The content structure of this dissertation is as follows:Chapter One:A brief historical retrospect on superconduction and high Tc superconductor, the discovery and experimental and theoretical progress on iron-based high Tc superconductors in time series.Chapter Two:Fundamental theories of specific heat and thermal conduction, and their applications on superconduction research and superconducting gap behavior in ultra-low temperature thermal conduction measurements.Chapter Three:An introduction to experimental facilities we are using, including PPMS system with specific heat option and ultra-low temperature thermal transport measurement system.Chapter Four:Report of specific heat research on iron-based superconductor of 1111 system-SmO1-xFxFeAs. Chapter Five:Report of specific heat research on iron-based superconductors of 122 system-Ba1-xKxFe2As2 and Ca1-xNaxFe2As2.Chapter Six:Report of ultra-low temperature thermal transport on electron-doped iron-based superconductor of 122 system-BaFe1.9Ni0.1As2.Chapter Seven:Report of ultra-low temperature thermal transport on iron-based superconductor of 11 system-FeSex.Chapter Eight:A conclusion of all our research works.更多还原