Raman and Other Optical Studies of Insulating Parent Phases of High Temperature Superconductors

技术摘要：铜超导体从一个强相关态演化而来，该态每个活性位点有一个载流子，是一个反铁磁绝缘体。当通过掺杂加入载流子时，相关效应被认为会导致高温超导。光子可以激发载流子对——一个双占据的铜位点加上一个空位点——或者一个载流子从铜轨道到同一位点上的另一个轨道。这些激发是由光子吸收、拉曼散射或自旋交换拉曼过程的中间状态产生的。为了更好地理解它们的行为，我们考察了它们的激发作为温度、掺杂和磁场的函数。非技术文摘：高温超导体的特性是由于电流载流子之间的强排斥相互作用。它们在铜原子之间移动，当每个铜原子恰好有一个载流子时，斥力会使载流子定位在铜的位置上。然后电传导停止；这种材料是绝缘体。为了移动载流子，必须提供有限的“量子”能量。这是通过光的吸附或散射光来实现的。研究了受激载流子的性质与温度、掺杂和磁场的关系。目标是详细了解绝缘相，从而更好地理解由此产生的超导状态。＊＊＊

9320892 Klein Technical abstract: Cuprate superconductors evolve from a strongly-correlated state which has one carrier per active site and which is an antiferromagnetic insulator. When carriers are added via doping, correlation effects are believed to cause high temperature superconductivity. Photons can excite carrier pairs - one doubly-occupied copper site plus one empty site - or a carrier from a copper orbital to another orbital on the same site. These excitations are produced by photon absorption, Raman scattering, or as the intermediate state of a spin-exchange Raman process. To better understand their behavior the excitations are probed as functions of temperature, doping and magnetic field. Non-technical abstract: High temperature superconductors owe their properties to strong repulsive interactions among the carriers of electric current. They move among copper atoms, and when each copper atom has precisely one carrier, repulsion causes the carriers to become localized on the copper sites. Electrical conduction then ceases; the material is an insulator. In order to move the carriers a finite "quantum" of energy has to be supplied. This is done via adsorption of light or by means of scattered light. The properties of the excited carriers is studied as functions of temperature, doping and magnetic field. The goal is to understand the insulating phase in detail and thereby better understand the superconducting state that results from it. ***