Theoretical Topics in Superconductivity and Graphene

超导体是一种携带电流而不耗散的金属。 这对于制造用于医学成像的大型电磁体是非常期望的性质。但这种磁铁目前只能在低温下工作。因此，它们需要冷藏。因此，找到适合于制造在室温下工作的磁体的材料是非常重要的。每隔几年就会发现新的超导体。一个重要的类别是铜酸盐，它们是保持记录临界温度值[Tc]高达约150开尔文的材料。最近还发现铁基金属具有超导性，我们希望研究它们的性质，以期提高Tc的值。 超导体并不是在技术应用中唯一重要的金属。电子工业也可以受益于新的半导体材料。在2004年，人们剥离了一层石墨，这是一种单原子厚的膜，具有令人惊讶的意外特性。作为一个例子，石墨烯中电荷载流子的运动由相对论性狄拉克方程控制。它们的移动性是极好的，并且已经提出了许多新颖的应用，例如显示屏中的元件。我们正在研究磁场下石墨烯的性质，以及它的性质如何取决于电子之间的库仑相互作用。这对于理解光与石墨烯片中电荷振荡的相互作用非常重要。还有其他具有不同和全新功能的新材料。这些包括单层MoS2，其是具有两个谷的直接带隙半导体。在这些材料中，有可能只从两个谷中的一个谷激发电子，而其他谷不受影响。我们计划研究它们的光学性质，目的是了解入射光如何在这些系统中变成充电电流。所有拟议的研究都涉及理论研究，旨在更好地微观理解最近发现的材料的性质。

Superconductors are metals which carry a current without dissipation. This is a very desirable property for making large electromagnets used in medical imaging. But such magnets presently work only at low temperatures. Hence they require refrigeration. So finding materials suitable for the fabrication of magnets that would operate at room temperature is very important. New classes of superconductors are discovered every few years. An important class is the cuprates which are the materials that hold the record critical temperature value [Tc] up to about 150 Kelvin. More recently Fe-based metals have also been found to superconduct and we wish to study their properties with a view at increasing the value of Tc. Superconductors are not the only metals of importance in technological applications. The electronic industry can also benefit from new semiconducting materials. In 2004, a single sheet of graphite was exfoliated which is a membrane a single atom thick and has amazing unexpected properties. As an example, the motion of the charge carriers in graphene is governed by a relativistic Dirac equation. Their mobility is excellent and many novel applications have been suggested such as elements in display screens. We are studying the properties of graphene under magnetic field and how its properties depend on the coulomb interactions between the electrons. This is important in understanding the interaction of light with the charge oscillations in the graphene sheets. There are also other new materials with different and quite new functionalities. These include a single layer MoS2 which is a direct gap semiconductor with two valleys. It is possible in these materials to excite electrons exclusively from one of the two valleys leaving the others unaffected. This could be very useful in applications to the communication industry .We plan to study their optical properties with an aim at understanding how incident light can be change to a charge current in these systems. All the proposed research involves theoretical studies aimed at better microscopic understanding of the properties of recently discovered materials.