Electronic Properties, Magnetotransport and STM in Quasi-One-and-Two-Dimensional Metals

这项研究涉及低维金属、半导体和半导体中电荷密度波(CDW)和自旋密度波(SDW)电子结构的研究。该研究利用扫描隧道显微镜(STM)和原子力显微镜(AFM)在单个原子的尺度上以分辨率探测原子和电子结构，并将结果与强磁场对某些材料的电子输运性质的影响的研究相关联。要研究的材料包括过渡金属硫化物，以及更复杂的晶体，如钽镍硒。上述技术的这种组合提供了与CDW、SDW和混合密度波相关的电子修饰的独特表征。它们还提供了对由杂质掺杂引起的CDW结构中的修改的极其灵敏的检测。三盐基化物的掺杂产生了新的电子相、金属-绝缘体转变和修饰的CDW，所有这些都可以用STM光谱、AFM扫描和强磁场输运来检测。结果应该提供对材料的电子性质的详细了解，这些材料由电子气中的密度波的存在以及由于杂质掺杂引起的电子密度波的变化而改变。%本研究中研究的高度各向异性金属和与密度波相关的不寻常的电子性质为材料的新电子修饰提供了洞察。通过扫描隧道显微镜(STM)和原子力显微镜(AFM)在原子尺度上研究这些性质，结合对强磁场中相关电子传导现象的宏观测量，可以对整个电子结构有一个独特的理解。STM和AFM研究提供了原子水平上的晶体结构和电子结构的图像。这些方法对杂质和缺陷的修饰非常敏感，可以用来系统地跟踪杂质原子的位置、有序和晶体中新电子相的形成。随之而来的电子和磁输运性质的改变将使原子组态和局部电子结构的变化与材料的整体电子响应相关联。这些方法的发展应该对新电子材料的设计和测试非常有用。

This research involves the study of electronic structure due to charge-density waves (CDWs) and spin-density waves (SDWs) in lower dimensional metals, semimetals and semiconductors. The research utilizes scanning tunneling microscopy (STM) and atomic force microscopy (AFM) to detect both the atomic and electronic structure with resolution on the scale of individual atoms and correlates the results with studies of the effects of high magnetic fields on the electronic transport properties of the some materials. The materials to be investigated include transition metal chalcogenides, as well as more complex crystals such as tantalum nickel selenide. This combination of the above techniques provides a unique characterization of the electronic modifications associated with CDWs, SDWs and mixed density waves. They also provide extremely sensitive detection of modifications in the CDW structure as induced by impurity doping. Doping of trichalcogenides produces new electronic phases, metal-insulator transitions and modified CDWs, all of which can be detected by STM spectroscopy, AFM scanning and high magnetic field transport. Results should provide a detailed understanding of the electronic properties of materials as modified by the presence of density- waves in the electron gas as well as changes in the electronic density waves due to impurity doping. %%% The highly anisotropic metals being studied in this research and the unusual electronic properties associated with density-waves provide insight into new electronic modifications of materials. Studies of these properties on an atomic scale by scanning tunneling microscopy (STM) and atomic force microscopy (AFM), combined with macroscopic measurements of the associated electronic conduction phenomena in high magnetic fields, lead to a unique understanding of the overall electronic structure. The STM and AFM studies provide a picture of both the crystal structure and the electronic structure at the atomic level. These methods are extremely sensitive to modifications by impurities and defects and can be used to systematically follow impurity atom locations, ordering and the formation of new electronic phases in the crystals. The accompanying modifications of the electronic and magnetotransport properties will correlate the changes in atomic configuration and local electronic structure with the overall electronic response of the material. The development of these methods should be extremely useful for the design and testing of new electronic materials.