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Behavior of Composite Fermions and the Stripe Phase Subjected to Short-Period Periodic Potential or Magnetic Field Modulation

复合费米子和条纹相在短周期电势或磁场调制下的行为

基本信息

批准号：
15540305
负责人：
ENDO Akira
金额：
$ 2.37万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

We have experimentally investigated the properties of short period (〜100 nm) unidirectional lateral superlattices in a magnetic field at low temperatures. Unidirectional lateral superlattice samples equipped with a back gate to control the electron density n_e have been fabricated. With these samples, we observed anisotropic magnetoresistance at high Landau levels, which was attributable to the response of the theoretically-predicted stripe phase (a charge density wave state) to the external modulation. We also found an unusual hysteretic behavior accompanying the variation of n_e.Transport properties of electrons at low magnetic fields have been explored in detail, which can be mapped to the properties of composite Fermions at low effective magnetic fields. We have found that the origin of the well-known positive magnetoresistance is mainly attributable to the drift velocity resulting from incompleted cyclotron orbits, and that the contribution of the channeled orbit is small, in contrast to what have been believed for some fifteen years.We have uncovered a new class of small-amplitude magnetoresistance oscillation superposed on the positive magnetoresistance. The new oscillation has been attributed, from its dependence on the period of the modulation and on n_e, to the geometric resonance between the modulation period and the width of the "open orbit" resulting from the Bragg reflection by the superlattice.We have studied the dependence of the modulation amplitude on n_e quantitatively, and have elucidated the effect of finite thickness of the two-dimensional electron gas on the amplitude.

实验研究了短周期（~ 100 nm）单向横向超晶格在低温磁场中的性质。制备了带有后门控制电子密度n_e的单向横向超晶格样品。在这些样品中，我们观察到了高朗道水平下的各向异性磁电阻，这是由于理论预测的条纹相位（电荷密度波状态）对外部调制的响应。我们还发现了伴随n_e变化的不寻常的滞后行为。对电子在低磁场下的输运性质进行了详细的研究，这可以映射到复合费米子在低有效磁场下的性质。我们发现，众所周知的正磁阻的起源主要是由于回旋加速器轨道不完整造成的漂移速度，而通道轨道的贡献是很小的，这与大约15年来所相信的相反。我们发现了叠加在正磁阻上的一类新的小振幅磁阻振荡。从调制周期和n_e的依赖性来看，新的振荡归因于调制周期和由超晶格布拉格反射引起的“开轨道”宽度之间的几何共振。我们定量地研究了调制振幅与n_e的关系，并阐明了二维电子气的有限厚度对振幅的影响。