权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Scanning tunneling microscopy studies on Andreev reflection and pseudogap in high-T_c cuprate superconductors

高温铜酸盐超导体中Andreev反射和赝能隙的扫描隧道显微镜研究

基本信息

批准号：
12640327
负责人：
ODA Migaku
金额：
$ 2.75万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

In the present study, we have performed tunneling spectroscopy and Andreev reflection experiments using scanning tunneling microscope (STM), and obtained the following results.1) In tunneling spectroscopy experiments, it has been found that in the lectronic excitations, there exist two kinds of pseudogaps (LPG and SPG) ; one with a characteristic energy comparable to the superconducting (SC) gap Δ and another one that is 3 to 4 times larger.2) The larger energy-scale pseudogap (LPG) develops progressively below higher crossover temperature T_<max>. On the other hand, the smaller energy-scale pseudogap (SPG) develops progressively below lower crossover temperature T* in addition to the LPG, and evolves smoothly into the SC gap below T_c. The SC gap amplitude Δ scales with T* in the entire carrier (hole) concentration region examined.3) In Andreev reflection experiments, it has been suggested that the Andreev gap, which has been considered to reflect the effective energy gapΔ_<eff>^ due to coherent pairing, scales with T_c.The above findings, combined with the results in angle-resolved photoemission experiments on the pseudogap evolution in the k-space, suggest that an energy gap around the so-called "cold spots", which opens below T_c, functions as the effective energy gap Δ_<eff>, and the carriers around me cold spots play an crucial role in establishing the long-range phase coherence in the collective motion of pairs.

本研究利用扫描隧道显微镜(STM)进行了隧道光谱和Andreev反射实验,得到了以下结果。1)在隧道光谱实验中,发现在电子激发下,存在两种赝能隙(LPG和SPG);一种具有与超导 (SC) 能隙 Δ 相当的特征能量，另一种则大 3 至 4 倍。2) 较大的能级赝能隙 (LPG) 在低于较高交叉温度 T_<max> 时逐渐发展。另一方面，除了LPG之外，较小的能级赝能隙（SPG）在较低的交叉温度T*以下逐渐发展，并在T_c以下平稳演化为SC能隙。在整个载流子（空穴）浓度区域中，SC 能隙幅度 Δ 与 T* 成比例。 3）在 Andreev 反射实验中，有人提出，Andreev 能隙被认为反映了由于相干配对而产生的有效能隙 Δ_<eff>^，与 T_c 成比例。上述发现，结合角度分辨光电子实验中关于赝能隙演化的结果 k 空间表明，在 T_c 以下打开的所谓“冷点”周围的能隙充当有效能隙 Δ_<eff>，并且冷点周围的载流子在建立电子对集体运动中的长程相位相干性方面发挥着至关重要的作用。