Study of quantum phase transition of two-dimensional dilute Bose gas by helium surface electrons

氦表面电子研究二维稀玻色气体的量子相变

基本信息

批准号：
16340108
负责人：
ARAI Toshikazu
金额：
$ 10.11万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

Two-dimensional dilute Bose gas is expected to undergo quantum phase transitions at low temperatures. The expected low temperature phase is quasi-condensate. The reduced density matrix of quasi-condensate vanishes as a power low. In that sense, quasi-condensate does not show a true off-diagonal-long range order but it has a quasi-long range order. It is pointed out that quasi-condensate exhibits superfluidity by Kosterlitz-Thouless mechanism, in which the system is stabilized by a formation of quantized vortex pair.With the aim of realize and observe superfluidity of two-dimensional dilute Bose gas, we cooled adsorbed two-dimensional atomic hydrogen gas on liquid helium surface. Hydrogen atoms are bounded on liquid helium surface and they lose the freedom of motion perpendicular to the surface while the motion along the surface is free. Since hydrogen atoms are Bosons, they form a two-dimensional Bose gas. Electrons, on the other hand, are also bounded on liquid helium surface and the … More system of helium surface state electrons (SSE) is a two-dimensional Coulomb gas. Since all the impurity is frozen below 1 K, the liquid helium surface is extraordinarily clean. By virtue of that, SSE exhibit very high mobility. We employed SSE as a probe to sense the state of adsorbed atomic hydrogen gas, expecting that the mobility of SSE would be ruled by collision with hydrogen atoms or excited quasiparticles.We embedded SSE in adsorbed hydrogen gas and measured its mobility. However, unfortunately, all the measured SSE mobility showed no difference between with or without adsorbed hydrogen gas. This may be because scattering cross section of electron-hydrogen collision is too small and SSE mobility is dominated by ripplon scattering regardless of the existence of hydrogen atoms.Although we have not yet observed two-dimensional superfluidity, we made good progresses in this research. We found that electron attachment to a hydrogen atom takes place when SSE is immersed in adsorbed atomic hydrogen and our precise measurement revealed the mechanism of the reaction. We developed pulse excited edgemagnetoplasmon technique which enabled fast SSE mobility measurement in strong magnetic fields. Recently, we found anomalous behaviors of edgemagntoplasmon signal at reduced SSE densities which cannot be explained by simple Drude model. The study of the anomalous behavior is in progress. Less

二维稀玻色气体预计会在低温下发生量子相变。预计的低温相是准凝聚态。从这个意义上说，准凝聚态的密度降低矩阵不会消失。表现出真正的非对角长程有序，但具有准长程有序。Kosterlitz-Thouless 指出准凝聚体表现出超流性。为了实现和观察二维稀玻色气体的超流性，我们对液氦表面吸附的二维原子氢气体进行了束缚。在液氦表面，它们失去垂直于表面的运动自由度，而沿表面的运动是自由的，因为氢原子是玻色子，它们形成二维玻色气体，另一方面，它们也被束缚在液氦表面上，氦表面态电子系统（SSE）是二维库仑气体，由于所有杂质都被冻结在 1 K 以下，因此液氦表面非常干净。因此，SSE表现出非常高的迁移率，我们采用SSE作为探针来感测吸附原子氢气的状态，期望SSE的迁移率由与氢原子的碰撞或激发决定。我们将SSE嵌入到吸附的氢气中并测量了其迁移率。然而，不幸的是，所有测量的SSE迁移率在有或没有吸附氢气的情况下都没有显示出差异，这可能是因为电子-氢碰撞的散射截面太小而导致。无论氢原子是否存在，SSE 迁移率均由波纹散射主导。尽管我们尚未观察到二维超流性，但我们在这项研究中取得了良好进展，我们发现电子附着在氢原子上。当 SSE 浸入吸附的原子氢中时，我们的精确测量揭示了反应机制。我们开发了脉冲激发边缘磁等离子技术，可以在强磁场中快速测量 SSE 迁移率。最近，我们发现在 SSE 密度降低的情况下边缘磁等离子信号的异常行为。无法用简单的德鲁德模型来解释。对该异常行为的研究正在进行中。