Theory of Solids

0089492艾伦该补助金支持对模仿真实的三维固体行为的模型的理论研究。 介观物理学的最新发展为研究强无序系统中的电或热输运提供了强大的新计算机算法。 将研究“电阻率饱和”现象，以检验“能带混合”效应参与并导致超出玻尔兹曼输运理论的天真预测的过度传导的假设。 一系列的模型将进行研究，越来越复杂的能带结构的数值。 晶格热传输中的一个类似问题是玻璃的导热率。 本文将用介观物理学的工具来处理非晶硅的一个现实的原子模型。有许多重要的氧化物材料具有钙钛矿（ABO 3）或相关的晶体结构，包括铁电体，高温超导体，离子导体电解质等。虽然大多数钙钛矿是绝缘体，少数是金属，并且相当多的具有作为掺杂或温度的函数的金属到绝缘体的转变。 Ba 1-xKxBiO 3和La 1-xCaxMnO 3系统是特别好的例子。 纯端元（x=0）化合物是绝缘材料的原型实例，因为基态对称性破缺，即BaBiO 3中的电荷有序，LaMnO 3中的轨道有序。 当掺杂水平x增加到临界值0.2-0.4时，这两种系统都成为感兴趣的金属。 对于参与这种金属到绝缘体转变的电子，存在很好的模型。 建议研究这些材料中的自陷态。 特别是，相反的端元（x=1）的CaMnO 3，当轻掺杂电子（x=1- 1）将被选为模型系统的研究之间的竞争自旋极化子效应和晶格极化子效应。 BaBiO_3和LaMnO_3的最低电子激发都是自陷激子。 这些将被研究和他们的新的光学性质（吸收光谱，共振拉曼光谱等）。将被预测。 当更重掺杂时，空穴应该自组织成平面反相边界带电缺陷（“条纹”的三维版本）。 这些将被研究和预测的属性。 金属-绝缘体转变作为掺杂的函数（极化子-玻璃崩塌）将被建模并仔细表征。%该补助金支持对氧化物材料的电学和热学性质的理论研究，这些材料由于其在温度和/或添加剂浓度变化时的复杂行为而具有极大的根本利益。 这些材料表现出丰富的效应，包括铁电性，高温超导性和离子导电性，可能会导致广泛的应用。

0089492AllenThis grant supports theoretical research on models which mimic the behavior of real three-dimensional solids. Recent developments in mesoscopic physics have provided powerful new computer algorithms for studying electrical or heat transport in strongly disordered systems. The phenomenon of "resistivity saturation" will be studied, in order to test the hypothesis that "band-mixing" effects are involved and cause the excess conduction beyond the naive prediction of Boltzmann transport theory. A series of models will be studied numerically with increasingly complex band structures. An analog problem in lattice heat transport is the thermal conductivity of glasses. A realistic atomistic model for amorphous silicon will be treated using the tools of mesoscopic physics.There are many important oxide materials with the perovskite (ABO3) or related crystal structures, including ferroelectrics, high temperature superconductors, ionic conductor electrolytes, etc. Although most perovskites are insulators, a few are metals, and quite a few have metal-to-insulator transitions as a function of doping or of temperature. The systems Ba1-xKxBiO3 and La1-xCaxMnO3 are particularly nice examples. The pure end-member (x=0) compounds are prototype examples of materials which are insulating because of a broken symmetry in the ground state, namely charge ordering in BaBiO3 , orbital ordering in LaMnO3 . Both systems become interesting metals when the doping level x increases to a critical value 0.2-0.4. Good models exist for the electons which participate in this metal-to-insulator transition. It is proposed to study self-trapped states in these materials. In particular, the opposite end-member (x=1) CaMnO3 , when lightly doped with electrons (x=1-epsilon) will be chosen as a model system for study of the competition between spin-polaron effects and lattice-polaron effects. The lowest electronic excitations of both BaBiO3 and LaMnO3 in this model are self-trapped excitons. These will be studied and their novel optical properties (adsorption spectra, resonant Raman spectra, etc.) will be predicted. When more heavily doped, holes should self-organize into planar anti-phase boundary charged defects (the three-dimensional version of "stripes"). These will be studied and the properties predicted. The metal-insulator transition as a function of doping (polaron-glass collapse) will be modeled and carefully characterized.%%% This grant supports theoretical research on the electrical and thermal properties of oxide materials which are of great fundamental interest due to their complex behavior as the temperature and/or concentration of additives is changed. These materials exhibit a wealth of effects including ferroelectricity, high temperature superconductivity and ionic conduction which may lead to widespread applications.***