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

二维稀玻色气体在低温下会发生量子相变。预期的低温相是准凝析相。准凝聚态的约化密度矩阵作为幂次函数消失。在这个意义上，准凝聚态并不表现出真正的非对角长程有序，但它具有准长程有序。本文指出准凝聚体具有超流性的机制是Kosterlitz-Escherless机制，即通过量子化涡旋对的形成来稳定系统.为了实现和观察二维稀玻色气体的超流性，我们对吸附在液氦表面的二维原子氢进行了冷却.氢原子被束缚在液氦表面上，失去了垂直于表面的运动自由度，而沿着表面的运动是自由的。由于氢原子是玻色子，它们形成二维玻色气体。另一方面，电子也被束缚在液氦表面， ...更多信息 氦表面态电子（SSE）系统是二维库仑气体。由于所有的杂质都在1 K以下冻结，液氦表面非常干净。由于这一点，SSE表现出非常高的流动性。我们用SSE作为探测吸附态氢原子的探针，期望SSE的迁移率受与氢原子或激发态准粒子碰撞的影响，将SSE嵌入吸附态氢原子中，测量了SSE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的氢气之间没有显示出差异。这可能是由于电子与氢原子碰撞的散射截面太小，而且无论氢原子的存在与否，SSE迁移率都是由ripplon散射决定的。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浸没在吸附的原子氢中时，电子附着到氢原子上，并且我们的精确测量揭示了反应的机理。我们开发了脉冲激发的边缘磁等离子体激元技术，使快速SSE迁移率测量在强磁场中。最近，我们发现边缘等离子体信号在降低的SSE密度下的异常行为不能用简单的Drude模型解释。对异常行为的研究正在进行中。少

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