Single Crystal Growth and Physical Characterization of Strongly Correlated Materials

在凝聚态物理学中研究的许多材料对电子之间的排斥库仑相互作用不敏感;简单的金属和半导体具有这种不敏感性。在这样的材料中，电子的动能主导电子-电子相互作用，这是泡利不相容原理和电子态的离域性质的结果。对于这些材料的电子行为可以用发展良好的微扰技术，如（kP）展开，局域密度近似和Hartree-Fock近似进行理论研究。相比之下，电子占据窄轨道的开放d和f电子壳层的材料受到排斥电子-电子相互作用的影响很大。这种强烈的库仑排斥导致电子在其轨道内的空间限制。这类材料被称为强关联材料。在强关联材料中，由于电子-电子相互作用使独立电子方法无效，标准微扰技术不再适用，而强关联材料的理论模型，如动态平均场理论（DMFT）仍处于起步阶段。为了进一步发展这些理论模型，重要的是研究和理解强关联材料的费米学。当材料转变为强关联相时，由于相之间的电子和磁序的差异，物理性质通常会发生显着的变化。与电子关联相关的现象的例子是金属-绝缘体转变、巨磁阻和超导性。这些现象可以导致技术进步，由此可控参数（例如温度、压力或场）的一些小的变化可以导致物理性质的显著变化，例如金属-绝缘体转变中的电导率的许多数量级的变化。这是一个准粒子的研究，由于相变后的相关电子性质的亚稳态寿命时间;准粒子在凝聚态物理学中形成了一个有趣的研究领域，尚未完全理解。这个博士项目将研究强关联材料的单晶生长和物理特性，以研究这类材料的费米学。X射线衍射将用于研究所生产材料的结构和相。电和磁输运性质将被研究，以调查性质的变化，样品过渡到强关联制度。费米面将通过de哈斯-货车阿尔芬效应，沿着与各向异性磁电阻和角分辨光电子能谱，以进一步了解所研究的材料的费米学的性质。强相关金属氧化物和浓缩铁磁半导体是两类强相关材料，将在本项目中进行详细研究，尽管随着项目的进展，可能会扩展到其他类别的强相关材料。

Many materials studied within condensed matter physics are insensitive to the repulsive Coulombic interactions between electrons; simple metals and semiconductors possess this insensitivity. In such materials the kinetic energy of electrons dominate the electron-electron interaction, this is a consequence of the Pauli exclusion principle and the delocalized nature of the electron states. For these materials the electronic behavior can be theoretically studied with well developed perturbative techniques such as the (k P) expansion, the local density approximation and the Hartree-Fock approximation. In comparison, materials with open d and f electrons shells with electrons occupying narrow orbitals are greatly affected by the repulsive electron-electron interaction. This strong Coulombic repulsion leads to spatial confinement of the electrons within their orbital. This class of material are called strongly correlated materials. In strongly correlated materials, standard perturbative techniques are no longer applicable due to the electron-electron interactions invalidating the independent-electron approach whilst theoretical models for strongly correlated materials, such as dynamical mean field theory (DMFT), are still in their infancy. To further develop these theoretical models it is important that the fermiologies of strongly correlated materials are investigated and understood.When a material transitions to the strongly correlated phase there is often a remarkable change in physical properties due to the difference in electronic and magnetic order between phases. Examples of the phenomena associated with electronic correlations are metal-insulator transitions, colossal magnetoresistance and superconductivity. These phenomena could lead to technological advancements whereby some small change in a controllable parameter e.g. temperature, pressure or field, can lead to a dramatic change in a physical property, such as a many orders-of-magnitude change in electrical conductivity in a metal-insulator transition. This is a quasiparticle study due to the metastable life times of the correlated electron properties following the phase transition; quasiparticles form an interesting field of study within condensed matter physics which has yet to be fully understood.This PhD project shall study the single crystal growth and physical characterization of strongly correlated materials in order to investigate the fermiology of this class of material. X-ray diffraction will be used to study the structures and phases of materials produced. Electro- and magneto- transport properties will be studied to investigate the change in properties as samples transition into the strongly correlated regime. The Fermi surfaces will be constructed via the de Haas- van Alphen effect, along with anisotropic magnetoresistance and angular resolved photoemission spectroscopy to further understand the nature of the fermiology of the materials studied. Strongly correlated metal oxides and concentrated ferromagnetic semiconductors are the two classes of strongly correlated material to be studied in detail within this project although expansion into other classes of strongly correlated material is possible as the project progresses.