Theory on band-gap control and correlation effects in semiconductors

通过减小直接半导体的带隙，增强了能带的非抛物性，实现了零带隙的线性色散狄拉克电子系统。进一步使带隙为负，可以得到半金属电子-空穴系统。我们研究了这些狄拉克和半金属电子-空穴系统中的关联效应。我们着重阐明了以下五个问题：(1)强磁场下石墨素的回旋共振；(2)密度不平衡的电子-空穴双层中的新型对凝聚；(3)半导体碳纳米管中的双激子和三子；(4)低维电子-空穴系统的全局相图；(5)能带狄拉克点的设计。

In decreasing the bandgap of the direct semiconductor, the nonparabolicity of the energy band is enhanced, and the Dirac electron system with linear dispersion is realized at zero band gap. Further making the bandgap negative, one could obtain the semimetallc electron-hole systems. We study the effect of correlation in these Dirac and semimetallic electron-hole systems. We particularly clarified the following five issues;(1) cyclotron resonance on grapheme under strong magnetic field(2) novel pair condensations in electron-hole bilayers with density unbalance(3) biexcitons and trions in semiconducting carbon nanotubes(4) global phase diagrams of low-dimensional electron-hole systems(5) Designing of Dirac points in energy band.