Direct observations of order parameters and microscopic analysis on phase transition

有序参数的直接观察和相变的微观分析

基本信息

批准号：
06452056
负责人：
HASEGAWA Tetuya
金额：
$ 3.14万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06452056/
关键词：
STM tunneling spectroscopy local density of states CDW Mott localization STM STS CDW 秩序パラメータ電荷移転科密度波

项目摘要

I proposed the atomic site tunneling (AST) spectroscopy which can obtained the tunneling spectrum specified on each atomic site by combining the scanning tunneling microscopy and tunneling spectroscopy Furthermore, I have succeeded in building up an AST apparatus by improving the mechanical strength of STM head and the electronics. As a model material suitable to the AST measurement, I selected 1T-Ta (S,Se)_2 system, which forms charge density waves below room temperature, and I have demonstrated the performance of AST measurements. In TaS_2, the AST data at room temperature showed slight site dependence, i.e., the tunneling spectra on the crest of CDW is rather metallic in comparison with those at the bottom of CDW.However, the over-all feature of the tunneling spectrum is quantitatively consistent with the band calculation. At77K,in contrast, the obtained tunneling spectra clearly shows a gap structure, and two conductance peaks at the gap edge is enhanced simultaneously on the crest of CDW.This implies that the density of states was transferred from the bottom to crest of CDW.The present tunneling result is a strong evidence for the Mott localization where electrons are localized due to the Coulomb interaction. In TaSe_2, I have not found the gap structure even at low temperatures. Namely, the band picture is essentially valid in this material. By replacing Se by S up to 1 : 1, the tunneling spectra suddenly varied, being consistent with the transport data. For Mott transition, there are two categories, i.e., effective mass diverges, or carrier concentration decreases to zero. I have not observed the zero bias conductance peak expected in the former case, suggesting the former mechanism.

我提出了原子位点隧道（AST）光谱，通过结合扫描隧道显微镜和隧道光谱，可以获得每个原子位点指定的隧道光谱。此外，我还通过提高STM头的机械强度和成功地构建了AST装置。电子产品。作为适合 AST 测量的模型材料，我选择了 1T-Ta (S,Se)_2 体系，它在室温以下形成电荷密度波，并演示了 AST 测量的性能。在TaS_2中，室温下的AST数据表现出轻微的位点依赖性，即与CDW底部的隧道谱相比，CDW顶部的隧道谱更具金属性。然而，隧道谱的整体特征是定量的与频带计算一致。相反，在77K时，获得的隧道光谱清楚地显示出带隙结构，并且带隙边缘的两个电导峰在CDW的波峰上同时增强。这意味着态密度从CDW的底部转移到波峰。目前的隧道效应结果是莫特局域化的有力证据，其中电子由于库仑相互作用而局域化。在TaSe_2中，即使在低温下我也没有发现带隙结构。也就是说，乐队图片在该材料中本质上是有效的。通过将 Se 替换为 S 高达 1:1，隧道光谱突然发生变化，与输运数据一致。对于莫特跃迁，有两类，即有效质量发散，或载流子浓度降至零。我没有观察到前一种情况中预期的零偏置电导峰值，这表明前一种机制。