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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

二维稀薄玻色气体有望在低温下发生量子相变。预期的低温相为准凝析相。准凝聚态的约化密度矩阵随着功率的降低而消失。在这个意义上，准凝聚态并不表现出真正的非对角线-长程有序，但它具有准长程有序。通过Kosterlitz-Thouless机制，指出准凝聚态的超流性是通过形成量子化的涡对来稳定的，为了实现和观察二维稀薄玻色气体的超流性，我们冷却了吸附在液氦表面的二维原子氢气。氢原子被束缚在液氦表面，失去了垂直于液氦表面运动的自由，而沿液氦表面的运动是自由的。由于氢原子是玻色子，所以它们形成了二维玻色气体。另一方面，电子也束缚在液氦表面和…上。莫尔氦表面态电子系统(SSE)是一种二维库仑气体。由于所有的杂质都冻结在1K以下，液氦表面非常干净。正因为如此，上交所表现出了非常高的流动性。我们利用SSE作为探针来探测吸附的氢原子的状态，期望SSE的迁移率由与氢原子或激发的准粒子的碰撞来决定，我们将SSE嵌入到吸附氢气中并测量了它的迁移率。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没有差别。这可能是因为电子-氢碰撞的散射截面太小，而且无论是否存在氢原子，单电子的迁移率都是以涟漪散射为主的。虽然我们还没有观察到二维超流，但我们在这方面的研究取得了很好的进展。我们发现，当SSE浸泡在吸附的原子氢中时，电子与氢原子发生了结合，我们的精确测量揭示了反应的机理。我们开发了脉冲激励的边缘磁浆激元技术，使在强磁场中快速测量SSE迁移率成为可能。最近，我们发现在SSE密度降低时，EDGE信号的反常行为，这不能用简单的Drude模型来解释。对这种异常行为的研究正在进行中。较少